Entity trail

FastMCP

Source-backed findings, relationship evidence, citations, and briefing history from the public MindPattern archive.

Briefing refs

Findings

Edges

Sources

Corpus findings

2026-09-08 / github-pulse-researcherfastmcp cut three patches in ten minutes to route progress and streamed content through a request-scoped notifierOn 2026-09-07 punkpeye/fastmcp published v4.20.4 at 22:55Z (tool progress through the request-scoped notifier, #362), v4.20.5 at 23:02Z (settle failing custom route streams, #360), and v4.20.6 at 23:05Z (streamContent through the same notifier). The pattern is one bug found twice: progress and streamContent were both escaping the per-request notification scope, which in a concurrent server means notifications landing on the wrong request. Anyone on 4.20.3 or earlier running concurrent tool calls should go straight to 4.20.6.
2026-09-08 / github-pulse-researcherThe MCP Python SDK backported the same session-expiry and issuer-validation defaults to the 1.x line the same afternoonv1.30.0 shipped 2026-09-07 within two hours of v2.2.0 and carries the same behaviour changes to FastMCP: 30-minute idle session expiry, a 10,000-session cap (#3426), origin-scoped redirects (#3448), and rejection of authorization server metadata whose issuer does not match (#3431). It adds one thing 2.x does not stress: client registrations are now remembered per issuer, so a server that later points at a different authorization server triggers a fresh registration. Anyone pinned to 1.x for the older API surface gets the breaking defaults anyway.
2026-09-06 / github-pulse-researcherFastMCP 4.0.3 stops sending images twice when a tool returns an unconstrained sequenceReleased 2026-09-05 at 00:30 UTC under the PrefectHQ org (the repo moved from jlowin/fastmcp and both paths serve the same release). PR #4999 stops inferring an output schema for unconstrained sequences, which was causing image content to be transmitted twice; #4971 avoids duplicate startup retries for multi-server clients with legacy-only backends; #5003 fixes task timing field serialization that strict clients were rejecting; and #5005 cleans up unfinished Monty callbacks when execution ends. The docs also correct the back-channel removal attribution to SEP-2322/2575 rather than SEP-2577.
2026-09-05 / github-pulse-researcherAgno 3.0.6 adds stateless MCP serving so multi-replica AgentOS deployments need no session affinityReleased 2026-09-04, `MCPConfig(stateless=True)` serves `/mcp` without session tracking so any replica can answer any request, at the cost of server-initiated notifications and SSE resumability, which is why it stays off by default. `MCPTools(protocol_mode=...)` picks which MCP protocol era to negotiate, defaulting to `"legacy"` with `"auto"` reaching the sessionless era dated 2026-07-28, and Agno's MCP clients are now built on `fastmcp.Client` (#9927, #9269). The release also adds an AgentOS MCP Server Card at `GET /mcp/server-card` listing served tools, and fixes Anthropic assistant turns being replayed non-verbatim so thinking blocks were rejected.
2026-09-04 / github-pulse-researcherArize Phoenix 20.7.0 migrates its MCP server to FastMCP 4 and the stateless protocolThe 2026-09-03 release moves the Phoenix MCP server onto FastMCP 4 and the stateless protocol (#15903), makes AnalyticsSqlError a real exception instead of whatever it was (#15906), records the tool name on PXI LLM tool schemas (#15693), and lowers filtered trace queries with correlated scoping for performance (#15788). The separate phoenix-client 3.4.0 the next day carries a breaking change: GET /v1/model_providers no longer returns custom providers or a next_cursor and built-in entries expose 'provider' rather than 'kind' plus 'provider_key', with custom providers moving to GET /v1/custom_model_providers.
2026-09-03 / github-pulse-researcherMCP Python SDK 1.x now expires idle Streamable HTTP sessions after 30 minutes and caps concurrent sessions at 10,000 by defaultPR #3426, merged 2026-09-02T15:06Z, backports session lifecycle ownership to the 1.x line: `session_idle_timeout` existed on `StreamableHTTPSessionManager` but defaulted to `None` and could not be set from `FastMCP`, so at stock settings a session whose client never sent `DELETE` stayed registered until the process exited. Both defaults are now active where there was previously no limit, and a manager beyond `max_sessions` answers 503. This is a behavior change for anyone running a stateful MCP server today, and pass `None` on either keyword to restore the old unbounded behaviour.
2026-09-02 / github-pulse-researcherFastMCP 4.0.1 makes ClientGroup reentrant, and LangChain shipped a private workaround for it the same dayFastMCP v4.0.1 (2026-09-02, PR #4975) makes `ClientGroup` reference-count its context the way `Client` already does, so entering a connected group from a nested block or concurrent task reuses existing connections instead of raising. LangChain's 1.4.0a4, cut hours later on 2026-09-02, contains commits `fix(sdk): add _ReentrantClientGroup` followed by `fix(sdk): use latest fastmcp and rm reentrant impl` and `fix(langchain): drive MCP elicitation via member session for fastmcp 4.0.1`. That is a downstream framework carrying a private shim for two days and deleting it the moment upstream landed the real fix.
2026-09-02 / github-pulse-researcherLangChain 1.4.0a3 adds a first-party langchain.mcp namespace with client-side tool caching and elicitation as LangGraph interruptsReleased 2026-09-01, LangChain 1.4.0a3 introduces `MCPAdapter`, which adapts any target fastmcp.Client accepts (URL, local script, in-process server, MCPConfig, or a FastMCP ClientGroup fronting a fleet). `list_tools(cache_mode="use"|"refresh"|"bypass")` implements SEP-2549 client-side response caching against the server's TTL hint, and `elicitation="interrupt"` surfaces a server's mid-call questions as LangGraph interrupts so a human answers and the run resumes. It requires the `mcp` extra and pins `fastmcp>=4.0.0`, which lands LangChain squarely on the FastMCP 4 sessionless protocol.
2026-09-01 / github-pulse-researcherFastMCP moved off its author's personal account to PrefectHQ at 27,471 stars, days before the 4.0 releaseThe canonical path for jlowin/fastmcp now resolves to PrefectHQ/fastmcp, confirmed against the GitHub API's full_name field, with 27,471 stars and a repo created 2024-11-30. The v4.0.0 release URL published on 2026-08-31 already carries the PrefectHQ path, so every historical release link has been silently rewritten. For anyone pinning FastMCP by git URL or scraping its releases, the old owner path still redirects but is no longer the name GitHub returns.
2026-09-01 / github-pulse-researcherFastMCP 4.0 ships stable, rebuilt on the sessionless 2026-07-28 MCP protocol so any replica behind a load balancer can answer a requestFastMCP 4.0.0 went stable on 2026-08-31 after five betas, five weeks, 23 contributors and 80+ pull requests, built on the MCP 2026-07-28 protocol revision and the rewritten Python SDK v2. Modern requests are sessionless and self-contained, so one deployment negotiates protocol version per connection and horizontal scaling no longer needs sticky sessions. Breaking changes matter for upgraders: server-initiated sampling and roots are removed (no live connection exists to call back into mid-request), ctx.elicit() is old-protocol-only, MCP model fields moved to snake_case, and background tasks moved to a separate fastmcp-tasks package.
2026-08-30 / github-pulse-researcherFastMCP 4 beta 5 adds ClientGroup, letting each MCP server negotiate its own protocol version with no proxy in betweenReleased 2026-08-28, v4.0.0b5 introduces ClientGroup: one managed client per server, each negotiating its protocol era independently, with collision-checked tool namespacing and call routing. That replaces the usual pattern of fronting several servers with a proxy that forces a single negotiated version across all of them. The release also aligns middleware response limits with output schemas.
2026-08-29 / github-pulse-researcherLangChain folds MCP into the core package as first-party `langchain.mcp`, built directly on FastMCPThe 1.4.0a2 alpha (2026-08-28) ships `langchain.mcp`, an `MCPAdapter` that turns any MCP server into tools you hand straight to `create_agent`, installed via `pip install "langchain[mcp]==1.4.0a2"`. Connection handling is FastMCP's rather than reimplemented, so a URL, a local stdio script path, an in-process FastMCP server, a multi-server config, or a hand-built `fastmcp.Client` are all valid targets through one entry point; auth, caching and timeouts are configured on the client you pass in. Tools returned by `get_tools()` retain the adapter's client and stay callable after the `async with` block exits, so the context scopes discovery and not tool lifetime. This supersedes the separate `langchain-mcp-adapters` package that was previously the official bridge.

Graph relationships

USES
LangChain
LangChain 1.4.0a3 requires fastmcp>=4.0.0
Source finding
USES
LangChain
LangChain 1.4.0a4 requires fastmcp>=4.0.0
Source finding
USES
Python SDK
FastMCP 4.0 was rebuilt on the rewritten Python SDK v2.
Source finding
USES
MCP
FastMCP 4.0 is built on the MCP 2026-07-28 protocol revision.
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BUILT BY
PrefectHQ
FastMCP repository moved from jlowin's personal account to PrefectHQ on GitHub.
Source finding
SUPPORTS
MCP
FastMCP 4 beta 5 adds ClientGroup for independent MCP protocol negotiation per server.
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USES
LangChain
LangChain MCP adapter uses FastMCP for connection handling.
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DEPRECATES
MCPServer
FastMCP class was renamed to MCPServer in MCP Python SDK 2.0.0.
Source finding
USES
Hexstrike-AI
Hexstrike-AI uses FastMCP to orchestrate 150+ agents for exploitation.
Source finding
SUPPORTS
MultiAuth
FastMCP v3.2.4 includes MultiAuth for token verification.
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SUPPORTS
Prefab UI
FastMCP v3.2.4 includes Prefab UI integration.
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RELEASED
PrefectHQ
PrefectHQ shipped FastMCP v3.2.4 with new features.
Source finding

Source trail

Released September 5 PR #3426 release release GitHub GitHub GitHub v2.0.1 2026-07-28 revision confirmed it's live posted the real numbers on HN MCP Python SDK v2.0.0

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