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chore(deps): update dependency fastmcp to v4 - #911

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chore(deps): update dependency fastmcp to v4#911
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renovate/fastmcp-4.x

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@renovate renovate Bot commented Sep 3, 2026 •
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This PR contains the following updates:

Package Change Age Confidence
fastmcp >= 3.0.0, < 4.0.0 → >=4.0.2, <4.1.0 age confidence
fastmcp >= 3.0.0, < 4.0.0 → >=4.0.2, <4.1.0 age confidence

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Some dependencies could not be looked up. Check the warning logs for more information.

Release Notes

PrefectHQ/fastmcp (fastmcp)

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

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.

♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

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

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renovate Bot requested review from DaveHanns and l2ysho as code owners September 3, 2026 12:36
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renovate Bot commented Sep 3, 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: uv.lock
Command failed: uv lock --upgrade-package fastmcp
Using CPython 3.14.7 interpreter at: /opt/containerbase/tools/python/3.14.7/bin/python3
  × No solution found when resolving dependencies for split (markers:
  │ python_full_version >= '3.14' and sys_platform == 'win32'):
  ╰─▶ Because fastmcp-slim[client]>=4.0.2 depends on mcp>=2.0.0,<3.0.0 and
      fastmcp>=4.0.2 depends on fastmcp-slim[client]==4.0.2, we can conclude
      that fastmcp>=4.0.2 depends on mcp>=2.0.0,<3.0.0.
      And because your project depends on fastmcp>=4.0.2 and
      mcp>=1.25.0,<2.0.0, we can conclude that your project's requirements
      are unsatisfiable.

hint: The resolution failed for an environment that is not the current one, consider limiting the environments with `tool.uv.environments`.

@renovate
renovate Bot force-pushed the renovate/fastmcp-4.x branch 3 times, most recently from 8b06950 to 6a0a1d3 Compare September 4, 2026 16:30
@renovate
renovate Bot force-pushed the renovate/fastmcp-4.x branch from 6a0a1d3 to 37cbaca Compare September 4, 2026 18:04
@l2ysho l2ysho mentioned this pull request Sep 4, 2026
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l2ysho commented Sep 4, 2026

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Superseded by #917, which bumps fastmcp to v4 together with the mcp v2 bump it requires, and ports python-mcp-proxy to the mcp 2 API. CI on #917 is green across all 58 jobs.

fastmcp 4 depends on mcp>=2.0.0,<3.0.0, so this PR's resolve was unsatisfiable against the mcp >= 1.25.0, < 2.0.0 pin left next to it — that is what renovate/artifacts and every Python lint/type-check leg were reporting.

🤖 Generated with Claude Code

@l2ysho l2ysho closed this Sep 4, 2026
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renovate Bot commented Sep 4, 2026

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Renovate Ignore Notification

Because you closed this PR without merging, Renovate will ignore this update. You will not get PRs for any future 4.x releases. But if you manually upgrade to 4.x then Renovate will re-enable minor and patch updates automatically.

If you accidentally closed this PR, or if you changed your mind: rename this PR to get a fresh replacement PR.

@renovate
renovate Bot deleted the renovate/fastmcp-4.x branch September 4, 2026 20:08
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