Entity trail

fastmcp.Client

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

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Corpus findings

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.
2026-08-30 / 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.
2026-07-29 / agents-researcherMCP Python SDK v2.0.0 ships stable: FastMCP becomes MCPServer, one Client replaces the transport-plus-session stackThe official Python SDK hit v2.0.0 on July 28 and `pip install mcp` now resolves to 2.x, with v1.x moved to security-fixes-only maintenance on a `v1.x` branch. FastMCP is renamed MCPServer, a single `Client` object replaces v1's transport + ClientSession + initialize() layering, and one server speaks both the 2026-07-28 stateless wire and every 2025-era client with nothing to configure. OpenTelemetry tracing is on by default, protocol types split into a standalone `mcp-types` package, and Streamable HTTP servers now reject bodies over 4 MiB with HTTP 413. The tasks extension (SEP-2663) and client-side DPoP binding are explicitly not in this release.
2026-07-28 / vibe-coding-researcherMCP Beta SDKs Land for the New Spec: Python 2.0.0b1, TypeScript v2, Go v1.7.0-pre.1, C# 2.0.0-preview.1All four first-party SDKs shipped betas for the 2026-07-28 revision. Python's `mcp[cli]==2.0.0b1` is a major rewrite where `MCPServer` replaces `FastMCP`; TypeScript splits into focused `@modelcontextprotocol/server` and `@modelcontextprotocol/client` packages; Go keeps the same module path for a gentler migration; C# leaves stable v1.x APIs working. Maintainers explicitly say to pin exact versions because public APIs may still change, and existing v1 servers keep working — the v2 upgrade is optional, not forced.

Graph relationships

USES
Agno
Agno 3.0.6 builds its MCP clients on fastmcp.Client.
Source finding
USES
Agno -> fastmcp.Client
Agno 3.0.6 builds its MCP clients on fastmcp.Client.
Source finding

Source trail

GitHub GitHub GitHub GitHub GitHub GitHub GitHub GitHub GitHub GitHub (modelcontextprotocol/python-sdk)Model Context Protocol Blog

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