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fix(deps): update dependency fastmcp to v4 - #721

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fix(deps): update dependency fastmcp to v4#721
renovate[bot] wants to merge 1 commit into
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renovate/fastmcp-4.x

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@renovate renovate Bot commented Sep 14, 2026

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This PR contains the following updates:

Package Change Age Confidence
fastmcp >=3.2.0,<4 → >=3.2.0,<5 age confidence

Release Notes

PrefectHQ/fastmcp (fastmcp)

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

Full Changelog: PrefectHQ/fastmcp@v3.4.7...v4.0.0

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🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

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@renovate
renovate Bot requested a review from a team as a code owner September 14, 2026 23:11
@renovate renovate Bot added bot Automated pull requests or issues dependencies Pull requests that update a dependency file renovate Pull requests from Renovate skip:codecov Skip Codecov reporting and check skip:test:long_running Skip long-running tests (≥5min) labels Sep 14, 2026
@renovate

renovate Bot commented Sep 14, 2026

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⚠️ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

♻ Renovate will retry this branch, including artifacts, only when one of the following happens:

  • any of the package files in this branch needs updating, or
  • the branch becomes conflicted, or
  • you click the rebase/retry checkbox if found above, or
  • you rename this PR's title to start with "rebase!" to trigger it manually

The artifact failure details are included below:

File name: pyproject.toml
Artifact update for fastmcp resolved to version 4.0.3, which is a pending version that has not yet passed the Minimum Release Age threshold.
Renovate was attempting to update to 4.0.0
This is (likely) not a bug in Renovate, but due to the way your project pins dependencies, _and_ how Renovate calls your package manager to update them.
Until Renovate supports specifying an exact update to your package manager (https://github.com/renovatebot/renovate/issues/41624), it is recommended to directly pin your dependencies (with `rangeStrategy=pin` for apps, or `rangeStrategy=widen` for libraries)
See also: https://docs.renovatebot.com/dependency-pinning/

@sonarqubecloud

sonarqubecloud Bot commented Sep 14, 2026

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Quality Gate Passed Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

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