# MCP Python SDK v2.0.0b1

- Product: MCP Python SDK (https://whatsnew.fyi/product/mcp-python-sdk)
- Vendor: Anthropic
- Date: 2026-06-30
- Version: v2.0.0b1
- Original notes: https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0b1
- Permalink: https://whatsnew.fyi/product/mcp-python-sdk/releases/v2.0.0b1
- 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'.

---

- **added** — First v2 beta with full support for the 2026-07-28 MCP specification
- **added** — ServerRunner as a pure handler kernel with thin transport drivers
- **changed** — FastMCP renamed to MCPServer with snake_case fields and constructor-based handler parameters
- **added** — New Client that auto-discovers server protocol version with server/discover and falls back to initialize
- **added** — Protocol types as standalone mcp_types package depending only on pydantic and typing-extensions
- **added** — Resolver dependency injection for tools to declare typed parameter requirements
- **added** — RFC 6570 URI templates for resource definitions with full operator set and path-security validation
- **added** — Extension APIs on both server and client sides with pluggable composition support
- **added** — Server middleware with (ctx, call_next) pattern and OpenTelemetry tracing with GenAI semantic conventions
- **added** — Stateless core with self-describing requests and server/discover without session handshake
- **added** — Multi-round-trip requests for tools, prompts, and resources to ask for input mid-call
- **added** — Header-based routing and caching with Mcp-Method, Mcp-Name, and Mcp-Param headers
- **added** — Subscriptions/listen with pluggable event bus support
- **added** — 2026-07-28 protocol negotiation over stdio with auto-mode for clients
- **added** — SEP-990 identity assertion (ID-JAG) for enterprise IdP flows
- **deprecated** — Roots, sampling, and logging/setLevel per SEP-2577 with advisory warnings only

First v2 beta, and the first release with full support for the [2026-07-28 MCP specification](https://blog.modelcontextprotocol.io/posts/2026-07-28-release-candidate/). Pre-releases are opt-in only; `pip install mcp` still resolves to the stable 1.x line.

```bash
pip install mcp==2.0.0b1
#### or
uv add "mcp==2.0.0b1"
```

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. Beta means the architecture is settled and changes from here should be much smaller than between alphas, but the API can still shift before stable v2, targeted for 2026-07-28 alongside the spec release - keep pinning an exact version.

##### What's new in v2

The whole v2 line so far (alphas included), condensed:

- **A new core.** The session-centric v1 internals are replaced by a dispatcher/runner pipeline built for the stateless 2026 protocol: `ServerRunner` is a pure handler kernel, transports are thin drivers over it, and one endpoint serves both protocol eras side by side.
- **`FastMCP` is now `MCPServer`.** The decorator API stays; the low-level `Server` takes handlers as constructor parameters, fields are snake_case, and traffic is validated against the negotiated spec version on the wire.
- **A new `Client`.** `Client(target, mode='auto')` speaks every protocol version - it probes `server/discover` and falls back to `initialize` automatically. The target can be a URL, a stdio subprocess, a custom transport, or a server object in memory (great for tests).
- **Protocol types are a standalone package.** `mcp-types` (imported as `mcp_types`) depends only on `pydantic` and `typing-extensions`, so tooling can speak MCP without the transport stack. Published in lock-step with `mcp`.
- **Resolver dependency injection.** Tools declare what they need as typed parameters; a resolver can compute the value server-side or ask the user, with questions delivered over elicitation on 2025 sessions and multi-round-trip requests on 2026 sessions.
- **RFC 6570 URI templates.** Resource templates support the full operator set - query parameters, path segments, explode modifiers - with path-security validation built in.
- **Extension APIs on both sides.** Servers compose protocol extensions - including MCP Apps - through a pluggable API; clients mirror it with `Client(extensions=[...])`.
- **Middleware and observability.** Server middleware is `(ctx, call_next)`, and OpenTelemetry tracing ships on by default with GenAI semantic conventions.
- **Docs rebuilt on tested examples.** Every snippet in the [book](https://py.sdk.modelcontextprotocol.io/v2/) is an executable, CI-tested file, plus a story-style examples suite and llms.txt renditions for agents.

##### 2026-07-28 spec support

Client and server:

- **Stateless core**: self-describing requests with no handshake, `server/discover`, scale-out on plain HTTP with no session affinity - progress and log notifications stream within the same single POST exchange.
- **Multi-round-trip requests**: tools, prompts, and resources can ask for input mid-call; clients auto-resolve through their existing callbacks; on `MCPServer`, `requestState` is sealed by default (authenticated encryption) so clients cannot read or forge it.
- **Header-based routing and caching**: `Mcp-Method` / `Mcp-Name` / `Mcp-Param-*` headers stamped by the client and validated by the server (SEP-2243), and `ttlMs` / `cacheScope` caching hints stamped by servers and honored by the client-side response cache (SEP-2549).
- **subscriptions/listen**: served with a pluggable event bus (SEP-2575); the client-side listen driver follows in a later pre-release.
- **2026-07-28 over stdio (#3038)**: auto-mode clients negotiate the new revision over stdio too - existing alpha clients upgrade with zero code changes.
- **Enterprise auth**: SEP-990 identity assertion (ID-JAG) for enterpri

_[Truncated at 4000 characters — full notes: https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0b1]_