[e2e] Expand Python conformance coverage

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

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Latest commit: 7881413

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7881413

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7881413

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7881413

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7881413

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7881413

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7881413

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready

[fantix]

Summary

Expands the Python workbench from a protocol smoke test into a cross-language conformance target driven by the existing TypeScript e2e suite.

• Ports 48 Python fixtures covering concurrency, sleeps, retries, errors, streams, hooks, child runs, metadata, and run attributes.
• Adds language-aware fixture and capability gating while keeping the shared test driver and assertions as the source of truth.
• Uses vercel-workflow directly, with the resolved vercel-py revision recorded in uv.lock.
• Simplifies the ASGI entrypoint and relies on the Vercel Python framework integration without a legacy builds override or the umbrella vercel package.
• Makes a small set of otherwise portable assertions language-neutral.

Why

Running the same driver against TypeScript and Python tests the actual cross-language contract: serialized inputs and outputs, durable event ordering, queue delivery, retries, hooks, streams, and CLI hydration. The conformance manifest also acts as a ratchet: once a Python fixture is enabled, removing it or regressing it fails the suite instead of silently skipping coverage.

Coverage

The enabled fixtures exercise:

• positional arguments, parallel steps, races, durable sleeps, cancellation, and resilient start;
• binary and structured streams, including writable handles forwarded to child runs;
• retry policy and serialized error identity and cause chains across step and workflow boundaries;
• hook metadata, repeated payloads, disposal, token reuse, conflicts, owner discovery, mutex, adoption, and forwarding patterns;
• child workflow creation and result retrieval;
• caught and uncaught unregistered-step failures;
• workflow and step attributes, including persistence when a run fails.

Known limitations

Two enabled tests have explicit capability exemptions in e2e-conformance.json:

• the final fire-and-forget attribute write does not begin before the Python workflow coroutine returns;
• reserved-attribute validation rejects the input correctly, but its message does not name the opt-in escape hatch expected by the shared assertion.

Fixtures that require Python APIs or failure semantics not implemented yet remain outside the enabled fixture list.

Validation

• Local Python conformance: 64 passed | 77 skipped (141)
• Vercel Python conformance: 62 passed | 98 skipped (160)
• pnpm build
• uv lock --check
• Preview deployment using only vercel-workflow

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7881413

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
example-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC
workflow-web	Ready	Preview, v0	Sep 1, 2026 3:12pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
workflow-docs	Skipped	v0	Sep 1, 2026 3:12pm UTC

[github-actions]

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

10 flaky tests

• an sfo1 reader sees chunks of an IN-PROGRESS iad1 stream (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (express)
• cancelRun via CLI - cancelling a running workflow (hono)
• FatalError fails immediately without retries (astro)
• outputStreamInsideStepWorkflow - getWritable() called inside step functions (vite)
• positive startIndex (skips first chunk) (vite)
• promiseAllWorkflow (nitro)
• sleepWinsRaceWorkflow (vite)
• workflow throw of a non-Error value round-trips verbatim as cause (nitro)
• workflow throw of a non-Error value round-trips verbatim as cause (tanstack-start)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

• cold-start-warmup · suite warmup (tanstack-start) · at 15:12:49Z · abandoned wrun_01M1EREPCY6PXC0YWAYEJHYAEK
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 15:17:31Z · abandoned wrun_01M1ERQH9T1B99QVKH246FRZ61
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 15:17:32Z · abandoned wrun_01M1ERQJGYJ9QETDS5BMXB39DE

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3632	0	688	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
✅ 🌐 Cross-language Conformance	64	0	77	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17179	0	2669	19848

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
✅ python-node	62	0	98
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	64	0	77

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay	violations
✅ smoke-no-steps	completed	3	0ms	ok	0
✅ smoke-one-step	completed	6	0ms	ok	0
✅ hook-at-step-started	completed	12	0ms	ok	0
✅ hook-at-step-completed	completed	12	0ms	ok	0
✅ hook-at-hook-created	completed	12	0ms	ok	0
✅ deadline-hook-wins	completed	7	1.0h	ok	0
✅ deadline-expires	completed	7	1.0h	ok	0
✅ long-sleep	completed	11	30.0d	ok	0
✅ hook-never-arrives	stalled	3	0ms	skipped	0
✅ step-retries-twice	completed	10	2.0s	ok	0
✅ parallel-steps	completed	9	0ms	ok	0
✅ hook-on-execution-state	completed	12	0ms	ok	0
✅ peek-hook-before-branch	completed	12	0ms	ok	0
✅ peek-hook-after-branch	completed	12	0ms	ok	0
✅ peek-hook-at-registration	completed	12	0ms	ok	0
✅ race-hook-before-probe	completed	12	0ms	ok	0
✅ race-hook-after-probe	completed	12	0ms	ok	0
✅ race-duplicate-delivery	completed	13	0ms	ok	0
✅ attr-hook-before-step	completed	11	0ms	ok	0
✅ attr-hook-after-step	completed	11	0ms	ok	0
✅ attr-from-step-body	completed	13	0ms	ok	0
✅ fork-hook-after-timeout	completed	14	1.0m	ok	0
✅ fork-hook-before-timeout	completed	14	1.0m	ok	0
✅ count-hook-after-timeout	completed	17	1.0m	ok	0
✅ count-hook-before-timeout	completed	20	1.0m	ok	0
✅ stale-read-step-count-fork	completed	20	1.0m	ok	0
✅ stale-read-equal-step-counts	completed	14	1.0m	ok	0
✅ step-vs-step-fork	completed	12	0ms	ok	0
✅ step-vs-step-fork-fenced	completed	12	0ms	ok	0
✅ fence-catches-benign-direction	completed	12	5ms	ok	0
✅ in-flight-before-decision	completed	17	1.0m	ok	0
❌ in-flight-before-decision-counted	completed	17	1.0m	ok	0
✅ in-flight-after-decision	completed	19	2.0m	ok	0
✅ stale-read-step-count-fork-fenced	completed	20	1.0m	ok	0
✅ fork-hook-wins	completed	13	1.0m	ok	0
✅ fork-timeout-wins	completed	13	1.0m	ok	0
✅ unclaimed-payload-under-fork	completed	17	1.0m	ok	0
✅ claimed-payload-under-fork	completed	17	1.0m	ok	0
✅ writers-independent-step-bodies	completed	12	0ms	ok	0
✅ writers-scripted-tempo	completed	12	0ms	ok	0
✅ cancel-mid-step	cancelled	7	0ms	skipped	0

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 7881413 · Tue, 01 Sep 2026 15:32:38 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	220 (+20%) 🔻	1370 🔴 (+29%) 🔻	1428 🔴 (+28%) 🔻	1768 🔴 (+24%) 🔻	30
TTFS	stream	228 (+6.0%)	1296 🔴 (+19%) 🔻	1406 🔴 (+28%) 🔻	1471 🔴 (+26%) 🔻	30
TTFS	hook + stream	1469 (+20%) 🔻	1565 🔴 (+17%) 🔻	1621 🔴 (+17%) 🔻	1798 🔴 (+15%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	599 (±0%)	2023 (+27%) 🔻	2105 (+20%) 🔻	2486 (+32%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1862 (+12%)	3730 (+12%)	3805 (+7.2%)	8061 (+21%) 🔻	10
STSO	1020 steps (inline)	125 (+13%)	160 (+8.1%)	185 (+6.3%)	257 (-27%) 💚	1019
WO	1020 steps	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	160029 (+7.4%)	1
CRTT	first chunk (pooled)	98 (+1.0%)	133 (-11%)	172 (±0%)	285 (+11%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	119 (-18%)	154 (-14%)	344 (-12%)	566 (-24%)	137 (-29%)	10
size sweep (100/s, 160B-12KB)	108 (-16%)	154 (-17%)	219 (-35%)	382 (-19%)	158 (+3%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	111 (-16%)	129 (-19%)	181 (-28%)	358 (-40%)	271 (-18%)	3
replay eve-gpt-5.6-sol-2000t (1x)	138 (-18%)	134 (-21%)	180 (-24%)	318 (-63%)	244 (-60%)	2
replay eve-gpt-5.6-sol-2000t (2x)	146 (+15%)	184 (-23%)	255 (-28%)	416 (-35%)	275 (-3%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 148790ms → this run 158789ms (Δ +9999ms, +7%)

100-150 ms ████████████████┃███████ main 779 this 556 -223
150-200 ms ██████░░░░░░┃ main 181 this 416 +235
200-250 ms ┃ main 31 this 35 +4
250-300 ms ┃ main 11 this 8 -3
300-350 ms ┃ main 6 this 2 -4
350-400 ms ┃ main 6 this 1 -5
400-450 ms ┃ main 1 this 1 +0
450-500 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
600-650 ms ┃ main 1 this 0 -1
650-700 ms ┃ main 1 this 0 -1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▄█▁▁··· 129 (-15%) 115 (-9%) 344 (-12%) 566 (-24%) 3000
sweep ······▄█▁···· 126.7 (-16%) 117 (-7%) 219 (-35%) 382 (-19%) 3000
gw 1x ·····▁▆█▁···· 115.6 (-16%) 106 (-12%) 181 (-28%) 358 (-40%) 5295
eve 1x ·····▁▆█▁···· 116.5 (-27%) 106 (-17%) 180 (-24%) 318 (-63%) 5186
eve 2x ·····▁▂█▃···· 154.7 (-18%) 138 (-16%) 255 (-28%) 416 (-35%) 7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control ▄▄▄▃▁▂██▄▂ 111–154ms
sweep ██▄▂▂▃▂▁▄▄ 109–157ms
gw 1x █▃▅▅▆▃▁▃▂█ 98–133ms
eve 1x ▅▁▂▂▃▄▅█▄▁ 101–141ms
eve 2x ▁▁▂▂▁▂▄█▃▃ 134–220ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep ▆██▅▃▂▁ 124–129ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control ▁▄▅▄▂█▄▄▂▅ 27–46ms
sweep ▁▅▅▁▅█▇▂▆▃ 45–54ms
gw 1x ▅▄▆▃▆▃▂▄▁█ 29–39ms
eve 1x █▃▄▂▇▆▇█▇▁ 21–26ms
eve 2x ▄▄▁▅▃▃▃▁▁█ 23–29ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​uvicorn@​0.52.3 ⏵ 0.52.4	+1

View full report

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.6 KiB (±0)	1.77 MiB (±0)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	765.6 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

7881413 · run

[fantix]

@vercel/workflow this PR is ready