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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteIf a Python wrapper that worked with the MCP SDK suddenly fails after an upgrade, check which mcp version was resolved before changing code. The official SDK now installs the stable 2.x line with pip install mcp. A wrapper developed for v1 can therefore receive v2 if its dependency requirement does not exclude it. For an unconverted package, the official migration guide says to keep an upper bound below 2 until migration is complete.
Why an SDK upgrade can break a wrapper
A wrapper library depends on the MCP Python SDK and may expose its own API on top of the SDK’s imports, classes, transports, and dependencies. If that wrapper was built against v1 but its package metadata allows any compatible future release—or otherwise has no upper bound below 2—a fresh installation or dependency update can resolve mcp to v2.
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The Model Context Protocol project’s v2.0.0 stable release is dated 2026-07-28, and its release record says pip install mcp now installs 2.x. That does not mean every wrapper is broken: a wrapper may already have migrated, may constrain its SDK dependency, or may work with both versions. Treat a major-version mismatch as a risk to investigate, not proof of the cause. MCP Python SDK v2 stable release
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Check the environment that actually runs the wrapper, its declared dependency, and the first failing import or call. A version number alone does not establish compatibility; compare the resolved version with the wrapper’s intended SDK range and use the traceback to identify where execution fails.
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- Check the installed version. Run
python -m pip show mcpin the same environment used to run the wrapper. Look at the reported version; do not assume your global Python installation matches a virtual environment, container, or deployment. - Inspect the wrapper’s dependency metadata. Check its package declaration and any constraints file for the
mcprequirement. An unbounded requirement or one that permits v2 is a clue if the wrapper has not migrated. - Inspect the lockfile and resolver output. Confirm which SDK and related dependencies were selected, and note any conflicts. A top-level version change may expose incompatible pins elsewhere in the environment.
- Read the first relevant traceback frame. An import error naming a moved module or renamed class suggests an API mismatch. A failure later in transport setup or response handling may instead involve changed dependency types or runtime behavior.
These checks narrow the diagnosis; they do not substitute for checking the wrapper’s own compatibility documentation or testing it with a coherent dependency set.
What changed between v1 and v2 that wrappers may rely on
The migration is broader than a single renamed import. The official guide distinguishes code changes from dependency changes, and the v2 overview also describes runtime and protocol behavior changes. The items below are diagnostic examples, not a complete inventory.
Imports and server APIs
The high-level server class was renamed from FastMCP to MCPServer, and its module moved. Old mcp.shared.* import paths and several low-level Server interfaces also changed or were removed. A wrapper that imports or re-exports these v1 symbols may fail during import or when constructing a server. Consult the migration guide for the complete symbol-by-symbol list. Migration guide: v1 to v2
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HTTP clients and transports
The HTTP client dependency changes from httpx and httpx-sse to httpx2. Transport keyword parameters largely remain, according to the migration guide, but code that passes a prebuilt client or authentication object may need the corresponding httpx2 type. The WebSocket transport and the mcp[ws] extra are also among the changes listed in the official material.
Dependency constraints and types
The migration guide’s example moves sse-starlette from >=2,<3 to >=3 when using mcp>=2,<3. If your project uses sse_starlette directly, account for that library’s own breaking changes as well. The guide also says opentelemetry-api becomes a hard dependency and mcp-types is exact-pinned to the SDK version; do not pin mcp-types independently.
Other removed or renamed items include deprecated transport spellings and callbacks. The migration guide is the authoritative checklist for a specific wrapper; a short list of examples cannot establish that every call site has been reviewed.
Runtime behavior
Even if imports work, v2 changes can affect behavior. The official overview notes stricter client response validation, RFC 6570 URI-template behavior, and a changed Streamable HTTP lifespan model. These are possible sources of runtime failures or changed assumptions, rather than evidence that every v1 wrapper will fail. What’s new in v2
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How to pin an unconverted wrapper back below v2
For a package that depends on mcp but has not migrated, the current official migration guide gives this requirement: mcp>=1.28,<2. It states: “If your package depends on mcp, keep a <2 upper bound until you’ve migrated.” Use that as a temporary compatibility constraint, not as a permanent substitute for migration. Model Context Protocol Python SDK migration guide
- Set the constraint in the right place. If you maintain the wrapper, update its declared dependency. If you are repairing an application that consumes it, use the project’s dependency or constraints mechanism so the resolver sees the v1 ceiling.
- Regenerate or restore a coherent environment. Re-resolve the lockfile, or restore a known-good lockfile and reinstall from it. Confirm that the installed
mcpversion is below 2 and that related packages satisfy their requirements. - Run the wrapper’s relevant tests or entry point. A successful installation only shows that dependencies resolved; it does not prove the wrapper’s behavior is correct.
- Handle resolver conflicts rather than forcing the SDK alone. The migration guide advises: “Relax or bump any conflicting pins when upgrading.” A failure to resolve can involve another pinned dependency, so changing just the top-level
mcprequirement may not be enough. - Track the migration separately. Use the complete official guide to update imports, API usage, dependencies, and runtime assumptions before removing the upper bound.
Choose between a temporary v1 pin and migrating to v2
| Path | When it fits | Trade-off |
|---|---|---|
Keep mcp>=1.28,<2 |
The wrapper has not been converted and restoring service takes priority. | It avoids an immediate v2 API migration, but v1 is in maintenance mode rather than the current stable line. |
| Migrate the wrapper to v2 | You can update the wrapper’s public API, implementation, and dependency constraints. | You must handle code and dependency changes and check for runtime behavior changes; the migration guide is the full checklist. |
The SDK project says v1.x remains in maintenance mode for critical bug fixes and security patches. That is a narrower commitment than ongoing feature development, so treat a v1 ceiling as a bridge while planning the migration, not as an assurance that v1 will receive every future change. MCP Python SDK v2 stable release
What the protocol revision date does—and does not—mean
The v2 release supports the protocol revision dated 2026-07-28 and serves earlier revisions from the same server, according to the release notes. The SDK’s major-version migration is a separate matter: the project’s beta announcement said existing protocol implementations were not switched off on that date. A wrapper failure after upgrading should therefore be investigated as a package, API, dependency, or runtime compatibility issue—not attributed automatically to the protocol date. Release notes SDK beta announcement and context
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