pypi / mcp-types

mcp-types

What changed in mcp-types 2, from its official release notes, upgrade guides and advisories. Sources checked 2026-10-21.

11 breaking1 security4 deprecations6 new APIs and options5 behavior and defaults5 fixes and other

See which of these apply to your code, ranked, in your agent:

npx @unstale/cli init

@unstale/cli 0.2.1 on npm

mcp-types 232 changes

Breaking changes 11

initialize leaves out experimental when none is configured; client code reading capabilities.experimental on a legacy connection should handle None.
2.3.0release notes
The required version is now httpx2>=2.10.0, up from >=2.5.0; the new max_sse_event_size option needs it.
2.3.0release notes
Empty _meta is omitted from outbound requests; on receiving connections, ctx.meta is None rather than {}.
2.3.0release notes
Requests without params omit the params member, and middleware sees ctx.params as None.
2.3.0release notes
Invalid tool header annotations now raise InvalidSignature at registration, naming the tool and the problem.
2.3.0release notes
MCP HTTP clients and OAuth providers follow redirects only within the endpoint's origin, with an http-to-https upgrade on the same host allowed. Other redirects fail instead of being followed.
2.2.0release notes
A 403 without an insufficient_scope challenge is returned to the caller rather than retried.
2.2.0release notes
On the legacy discovery path, authorization server metadata is rejected when its issuer differs from the server's origin.
2.2.0release notes
Tool schema $refs resolve only within that schema; an unresolvable reference raises RuntimeError: Invalid schema for tool ....
2.2.0release notes
If fetching protected resource metadata fails with a 5xx or 429, the OAuth flow stops instead of falling back to legacy endpoints.
2.2.0release notes
Idle stateful Streamable HTTP sessions using the legacy spec now expire after 30 minutes; set session_idle_timeout=None to disable expiration.
2.2.0release notes

Security 1

Controls whether only tokens that the TokenVerifier reports as issued for this server are accepted.
2.2.0release notes

Deprecations 4

When resource_server_url is set, leaving validate_token_resource unset emits an MCPDeprecationWarning; set it to True or False because 3.0 defaults it to True.
2.2.0release notes
Constructing this provider without issuer= emits an MCPDeprecationWarning; pass the authorization server's issuer URL because 3.0 will require it.
2.2.0release notes
Constructing this provider without issuer= emits an MCPDeprecationWarning; pass the authorization server's issuer URL because 3.0 will require it.
2.2.0release notes
Imports of mcp.server.fastmcp point to the migration guide, helping developers address the import warning.
2.0.1release notes

New APIs and options 6

Server accepts get_tool_input_schema so a low-level server can supply a tool schema for header validation without running its tools/list handler.
2.3.0release notes
Added to streamable_http_client and StreamableHttpParameters; the default remains 1 MiB per SSE event, and None or a larger value permits larger tool results.
2.3.0release notes
MCPServer(subscriptions=False) stops serving subscriptions/listen and advertises listChanged and subscribe as false.
2.3.0release notes
Adds issuer= for specifying the authorization server's issuer URL.
2.2.0release notes
Streamable HTTP servers now hold at most 10,000 sessions; set max_sessions=None to disable the cap.
2.2.0release notes
Adds issuer= for specifying the authorization server's issuer URL.
2.2.0release notes

Behavior and default changes 5

Context[AppState] now works on prompts and resource templates, as well as tools.
2.3.0release notes
Validation looks up the registered tool schema by name instead of running tools/list for each tools/call; list middleware no longer affects validation.
2.3.0release notes
Request timeouts pause while OAuthClientProvider waits on redirect_handler and callback_handler, so an interactive login no longer counts against them.
2.3.0release notes
Client spans now record JSON-RPC error responses; with mode="auto", probing a server without server/discover shows one ERROR span.
2.3.0release notes
A client DELETE now frees its session immediately.
2.2.0release notes

Fixes and other changes 5

After a HeaderMismatch (-32020) rejection, the client re-lists tools and retries the call once.
2.3.0release notes
A raising progress_callback no longer fails a call on an in-process Client(server).
2.3.0release notes
On Windows, stdio_client resolves the executable off the event loop.
2.3.0release notes
An explicit structuredContent null is now checked against the output schema instead of being treated as missing.
2.3.0release notes
A refused opening request no longer leaves a session behind.
2.2.0release notes