🤖 feat: custom providers can choose their LLM API format by ibetitsmike · Pull Request #3938 · coder/xum

ibetitsmike · 2026-08-23T22:05:54Z

Summary

Custom providers can now choose their LLM API format. The custom-provider providerType field, previously locked to "openai-compatible", accepts three values that select the SDK adapter and wire format: openai-compatible (Chat Completions via @ai-sdk/openai-compatible, still the default), openai-responses (OpenAI Responses API via @ai-sdk/openai), and anthropic-messages (Anthropic Messages via @ai-sdk/anthropic). The Settings UI gains an "API format" selector in the add form and on each custom provider card.

Fixes#3934

Background

LLM gateways expose different models behind different API formats (e.g. OpenCode Zen serves some models over Chat Completions and others over Anthropic Messages). Built-in openai/anthropic providers already accept a custom baseUrl, but custom-named provider entries were hardcoded to the OpenAI-compatible Chat Completions path at every layer (schema, guards, ProviderService, model factory).

Implementation

CUSTOM_PROVIDER_TYPES in customProviders.ts is the single source of truth; the config schema, oRPC schemas, guards, and UI labels derive from it. The isCustomOpenAICompatible* helper family is renamed to format-agnostic isCustomProviderConfig/getCustomProviderIds/etc. since membership/shadowing semantics are identical for all custom types.
The model factory's custom branch switches on providerType: the existing createOpenAICompatible path is unchanged; the two new paths reuse the lazy PROVIDER_REGISTRY loaders and the format-appropriate base URL normalization (/v1 handling differs between the OpenAI-shaped and Anthropic adapters). Custom adapters always receive an explicit apiKey so the official SDKs cannot silently fall back to OPENAI_API_KEY/ANTHROPIC_API_KEY env vars and leak real credentials to a third-party gateway. The anthropic-messages path reuses the prompt-cache cache_control fetch wrapper.
addCustomOpenAICompatibleProvider is renamed to addCustomProvider and accepts an optional providerType (default openai-compatible); setProviderConfig accepts providerType edits validated against the enum. Existing configs parse and behave identically; no migration.
Tests: schema/guard/service/factory unit coverage plus IPC integration tests that stream through a local mock server and assert the request path per format (/v1/chat/completions, /v1/responses, /v1/messages). A shared happy-dom SelectPrimitive double (tests/ui/selectPrimitiveDouble.tsx, extracted from the advisor settings test) makes the Radix Select interactions testable.

Validation

make static-check, touched unit suites, and TEST_INTEGRATION=1 bun x jest tests/ipc/providers/openaiCompatible.test.ts all green locally.
Remote dogfood UAT on this exact commit: PASS. All three formats were added through the real UI, wire formats proven against a mock server per endpoint path, format editing on an existing provider took effect without restart, hand-written legacy openai-compatible entries and built-in provider cards regression-checked, and a real-model smoke chat succeeded.

Risks

Low for existing setups: the openai-compatible path and its base URL normalization are byte-for-byte unchanged, and providerType still defaults to it everywhere. The new paths reuse the built-in providers' adapters. Main regression surface is the guard renames touching provider shadowing/routing checks; those are mechanical and covered by existing tests.

Generated with xum • Model: anthropic:claude-fable-5 • Thinking: xhigh

…-responses, anthropic-messages)

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ibetitsmike · 2026-08-23T22:06:16Z

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…ormat edits, UI resync on failed persistence)

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…adapters, tools identity wire remap, in-lock shadow recheck, drop manual useMemo)

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…apters, store policy, raw-identity metadata, cache classification, keyless auth headers, drop useCallback)

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…ptions, Anthropic base URL path normalization)

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…advisor createModel so alias metadata survives the wire remap)

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…he wire when Anthropic beta features are disabled)

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All three SDK adapters (@ai-sdk/anthropic, @ai-sdk/openai, @ai-sdk/openai-compatible) build request URLs by appending the endpoint path directly onto the base URL string, so a query or fragment swallows the endpoint (https://proxy.example/v1?token=x -> .../v1?token=x/messages). Reject such base URLs at addCustomProvider, setConfig baseUrl edits, and the add form instead of silently stripping them: auth query params can never work with these adapters, and stripping would surface as a confusing request-time 401.

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Summary

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