# AN-2026-0846: MCP Python SDK 2.0.0 (Jul 28, 2026): `pip install mcp` now installs v2 and v1.x gets security fixes only; unpinned "mcp" requirements pick up the breaking v2 API (pin mcp>=1.28,<2 to stay on v1)

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- id: AN-2026-0846 (version 1; cite https://breakwire.org/claim/AN-2026-0846/v/1)
- kind: breaking · status: active · review: editor
- source: <https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0>
- more sources: <https://py.sdk.modelcontextprotocol.io/v2/migration/> <https://pypi.org/project/mcp/2.0.0/>
- event date: 2026-07-28
- services: mcp-python-sdk, mcp, python
- affected: pypi:mcp >=2.0.0
- severity: high
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The v2.0.0 release notes (published 2026-07-28) say v2.0.0 is the stable v2 release of the MCP Python SDK, that it supports the 2026-07-28 revision of the Model Context Protocol, and that `pip install mcp` now installs 2.x.  [✓0 ✗0]
1. The release notes say v1.x is in maintenance mode and will only receive security fixes; the 1.x line lives on the v1.x branch and is documented at https://py.sdk.modelcontextprotocol.io/v1/.  [✓0 ✗0]
2. The release notes advise projects not ready to migrate to keep a <2 upper bound on the requirement, for example mcp>=1.28,<2, and point to the migration guide, which lists every breaking change with before-and-after code.  [✓0 ✗0]
3. The migration guide says v2 raises dependency floors (anyio >=4.9, pydantic >=2.12, sse-starlette >=3.0.0, typing-extensions >=4.13.0), adds required opentelemetry-api, mcp-types (exact-pinned) and httpx2, and removes httpx, httpx-sse and the ws extra; a project pinning one of these below the new floor fails resolution ("No solution found when resolving dependencies" in uv).  [✓0 ✗0]

## Fix
```text
Pin `mcp>=1.28,<2` until the code is migrated, then follow the v2 migration guide (https://py.sdk.modelcontextprotocol.io/v2/migration/) section by section; the standalone `fastmcp` package is a different project and is not covered by this change.
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0846/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28