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Update dependency fastmcp to v4 - #402

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Update dependency fastmcp to v4#402
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renovate/fastmcp-4.x

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@renovate renovate Bot commented Sep 5, 2026 •
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This PR body was truncated due to platform limits.

This PR contains the following updates:

Package Change Age Confidence
fastmcp >=3.0.1,<4 → >=4.0.3,<5 age confidence

Release Notes

PrefectHQ/fastmcp (fastmcp)

v4.0.3: : Once Is Enough

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Multi-server clients with legacy-only backends now avoid unnecessary startup retries, and tools returning unconstrained sequences no longer send images twice. This patch also fixes task timing values rejected by strict clients and cleans up unfinished Monty callbacks when execution ends.

What's Changed

Enhancements ✨
Fixes 🐞
Docs 📚

New Contributors

Full Changelog: PrefectHQ/fastmcp@v4.0.2...v4.0.3

v4.0.2: : Root Access

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ClientGroup is now importable from the package root, from fastmcp import ClientGroup, with the same lazy export and install hint as Client, so integrations no longer couple to FastMCP's internal module layout.

What's Changed
Enhancements ✨
Fixes 🐞
Docs 📚
Other Changes 🦾

Full Changelog: PrefectHQ/fastmcp@v4.0.1...v4.0.2

v4.0.1: : Come Back Any Time

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ClientGroup now reference-counts its context the way Client does, so entering a connected group from a nested block or a concurrent task reuses the existing connections instead of raising. Adapters written against Client's reentrancy can hold a ClientGroup the same way.

What's Changed

Fixes 🐞
Docs 📚
Other Changes 🦾

Full Changelog: PrefectHQ/fastmcp@v4.0.0...v4.0.1

v4.0.0: : Four Real

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FastMCP 4 is stable. Five betas, five weeks, 23 contributors, and more than 80 pull requests later — the new protocol engine held up under real gateways, agent frameworks, and production servers, and most FastMCP 3 applications upgrade without code changes.

This is the FastMCP release for the new MCP. On July 28, MCP released the 2026-07-28 protocol revision and the rewritten Python SDK v2 shipped the same day. FastMCP 4 is built on both: modern requests are sessionless and self-contained, so any replica behind an ordinary load balancer can answer them, and one FastMCP 4 deployment negotiates the best protocol version per connection — new clients get the new protocol, old clients keep working, and Client(url) does the same negotiation from the other side.

The new protocol's capabilities come through FastMCP's usual high-level surfaces:

  • Interactive tools return a request for input — approval, a missing field — and re-run with the client's answers available on the context.
  • Background tasks (@mcp.tool(task=True)) run outside the request path via the io.modelcontextprotocol/tasks extension, shipped in the optional fastmcp-tasks package on the same Docket engine as FastMCP 3.
  • Extensions register with add_extension(): a negotiated capability, additive request methods, tool-call interception, and a lifespan. Tasks are built this way, outside core.
  • Argument completion for prompt and resource-template inputs, with already-supplied arguments visible to the handler.
  • Auth for agents and services: identity assertion (SEP-990, beta), provider-neutral role checks, insufficient-scope challenges that name the missing scopes, and client-credentials auth.
  • Infrastructure hooks: server-level cache hints, and Mcp-Method/Mcp-Name routing headers so gateways can route without parsing JSON-RPC.

The framework grew alongside the protocol: dependency injection can bind a dependency to arguments of the call it serves (Depends(get_account, user_id=CallArgument("owner"))) while keeping it out of the tool schema, and ClientGroup manages one client per server with collision-checked namespacing — each member negotiating its own protocol version.

The beta period motivated a bunch of correctness work. Most of it was auth: hardened OAuth consent flows, issuer validation, and JWT verification, plus proxies that strip cookies and connection-owned headers at trust boundaries. The rest was durability and compatibility — encrypted task snapshots, serialized event-store writes, response caching handling empty results, errors, and versioned components, and dozens of smaller fixes from CodeMode to Python 3.14 compat.

Breaking changes: server-initiated sampling and roots are removed (no live connection exists to call back into mid-request), ctx.elicit() is old-protocol-only, FastMCP 3's deprecated APIs are gone, MCP model fields are snake_case (with a warning compatibility bridge for the old names), and background tasks moved to fastmcp-tasks. Passing a bare string like Client("server.py") to run local code is deprecated in favor of Path, for removal in FastMCP 5.

The upgrade guide covers every change and includes a copyable prompt for auditing an application with a coding agent.

Happy (context) engineering!

What's Changed

New Features 🎉
Breaking Changes ⚠️
Enhancements ✨
Security 🔒
Fixes 🐞
Docs 📚
Dependencies 📦
Other Changes 🦾

New Contributors

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This PR was generated by Mend Renovate. View the repository job log.

@renovate renovate Bot added the renovate label Sep 5, 2026
@renovate renovate Bot changed the title Update dependency fastmcp to v4 Update dependency fastmcp to v4 - autoclosed Sep 5, 2026
@renovate renovate Bot closed this Sep 5, 2026
@renovate
renovate Bot deleted the renovate/fastmcp-4.x branch September 5, 2026 06:02
@renovate renovate Bot changed the title Update dependency fastmcp to v4 - autoclosed Update dependency fastmcp to v4 Sep 5, 2026
@renovate renovate Bot reopened this Sep 5, 2026
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renovate Bot force-pushed the renovate/fastmcp-4.x branch 2 times, most recently from 7d34ccc to d2dac52 Compare September 5, 2026 09:56
@renovate
renovate Bot force-pushed the renovate/fastmcp-4.x branch from d2dac52 to f8062bd Compare September 7, 2026 17:37
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