# MCP Python SDK v2.0.0rc1

- Product: MCP Python SDK (https://whatsnew.fyi/product/mcp-python-sdk)
- Vendor: Anthropic
- Date: 2026-07-27
- Version: v2.0.0rc1
- Original notes: https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0rc1
- Permalink: https://whatsnew.fyi/product/mcp-python-sdk/releases/v2.0.0rc1
- Labels: Pre-release

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

---

- **changed** — Client(cache=False) is now Client(cache=None); CacheConfig() is the default and None switches the response cache off
- **removed** — Context.client_id is removed; read _meta via ctx.request_context.meta or the authenticated client via get_access_token().client_id
- **removed** — RFC7523OAuthClientProvider and JWTParameters are removed; use ClientCredentialsOAuthProvider, PrivateKeyJWTOAuthProvider, or IdentityAssertionOAuthProvider
- **changed** — Client-credentials OAuth providers now take scope= instead of scopes=
- **removed** — OAuthClientProvider(timeout=...) parameter is removed
- **changed** — message_handler receives ServerNotification | Exception only; the RequestResponder arm and mcp.shared.session module are removed
- **changed** — FileResource(is_binary=...) is replaced by encoding: str | None
- **removed** — MCP_* environment variables no longer configure MCPServer and pydantic-settings is dropped from runtime dependencies
- **changed** — Streamable HTTP servers reject request bodies over 4 MiB with HTTP 413; raise max_request_body_size to accept larger messages
- **changed** — Request-side clientInfo _meta key is now optional; serverInfo moved out of server/discover result body into every 2026-era result's _meta
- **changed** — client.server_info is now Implementation | None
- **added** — stdio server decides the protocol era from the client's opening request, enabling subscriptions/listen and other 2026-07-28 features over stdio
- **changed** — stdio_server() serves from private duplicates of stdin/stdout and points file descriptors 0 and 1 away from the JSON-RPC stream to prevent corruption from stray output
- **changed** — Tool results validated against an output schema are now much faster with compiled and cached JSON Schema validator

First v2 release candidate. Pre-releases are opt-in only; `pip install mcp` still resolves to the stable 1.x line.

```bash
pip install mcp==2.0.0rc1
#### or
uv add "mcp==2.0.0rc1"
```

The [documentation](https://py.sdk.modelcontextprotocol.io/v2/) has the full tutorial and API reference, and the [migration guide](https://py.sdk.modelcontextprotocol.io/v2/migration/) covers coming from v1. Stable v2 is planned for 2026-07-28 alongside the spec release - keep pinning an exact version until then.

##### Highlights

###### API cleanup ahead of stable (breaking for beta users)

The last pre-release pass over the public surface; every item has a migration guide entry.

- `Client(cache=False)` is now `Client(cache=None)`: `CacheConfig()` is the default and `None` switches the response cache off (#3164).
- `Context.client_id` is removed - read `_meta` via `ctx.request_context.meta`, or the authenticated client via `get_access_token().client_id` (#3167).
- `RFC7523OAuthClientProvider` and `JWTParameters` are removed - use `ClientCredentialsOAuthProvider`, `PrivateKeyJWTOAuthProvider`, or `IdentityAssertionOAuthProvider` (#3169).
- The client-credentials providers take `scope=`, not `scopes=` (#3166).
- `OAuthClientProvider(timeout=...)` is removed; it never bounded anything (#3165).
- `message_handler` receives `ServerNotification | Exception` only; the dead `RequestResponder` arm and the `mcp.shared.session` module are gone (#3168).
- `FileResource(is_binary=...)` is replaced by `encoding: str | None` (#3171).
- `MCP_*` environment variables never configured `MCPServer` and are no longer advertised; `pydantic-settings` is dropped from the runtime dependencies (#3170).
- Streamable HTTP servers reject request bodies over 4 MiB with HTTP 413; raise `max_request_body_size` if you accept larger messages (#3095).

###### Aligned with the final 2026-07-28 identity shape (#3143)

The request-side `clientInfo` `_meta` key is optional (the required pair is `protocolVersion` + `clientCapabilities`), and `serverInfo` moved out of the `server/discover` result body into every 2026-era result's `_meta`; `client.server_info` is now `Implementation | None`. This tracks spec change [#3002](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/3002) and fixes interop with servers that already omit body `serverInfo`.

###### The full 2026-07-28 revision over stdio (#3152)

A stdio (or in-memory) server now decides the protocol era from the client's opening request, so `subscriptions/listen` and every other 2026-07-28 feature serve over stdio, not only Streamable HTTP.

###### stdio servers keep handlers off the wire (#3117)

`stdio_server()` serves from private duplicates of stdin/stdout and points fd 0 at the null device and fd 1 at stderr while it runs, so a stray `print()` or a chatty child process can no longer corrupt the JSON-RPC stream. This fixes the classic print-corrupts-the-wire class ([#409](https://github.com/modelcontextprotocol/python-sdk/issues/409)) and the Windows tool-call hang ([#671](https://github.com/modelcontextprotocol/python-sdk/issues/671)).

##### Notes

- Tool results validated against an output schema are much faster: the JSON Schema validator is compiled once and cached (#3134).
- The tasks extension (SEP-2663) is not in this release, and will not be in v2.0.0.
- If you install under uv's `exclude-newer` cooldown: `mcp` pins `mcp-types` to the exact same version, so exempt both packages - `exclude-newer-package = { mcp = false, mcp-types = false }`.


##### What's Changed
* Add Streamable HTTP request body limits by @Kludex in https://github.com/modelcontextprotocol/python-sdk/pull/3095
* docs: document Windows stdio subprocess stdin handling by @AndreKalberer in https://github.com/modelcontextprotocol/python-sdk/pull/3079
* docs: make API reference rendering independent of page order by @maxisbey in https://github.com/modelcontextprotocol/python-sdk/pull/3107

_[Truncated at 4000 characters — full notes: https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0rc1]_