Add VERSIONING.md, ROADMAP.md, and DEPENDENCY_POLICY.md

Add standalone policy/governance files to match the TypeScript SDK's
structure (PR #1547). These files are checked by the tier-check CLI.

- VERSIONING.md: semver policy adapted for Python (compatible-release
  specifiers, DeprecationWarning, Python version support)
- ROADMAP.md: spec tracking and v2 milestones (shared across SDKs)
- DEPENDENCY_POLICY.md: extracted from CONTRIBUTING.md and expanded
  with policy rationale (update triggers, automated tooling, pinning)
- CONTRIBUTING.md: updated to reference standalone DEPENDENCY_POLICY.md

Author: felixweinberger

CONTRIBUTING.md

@@ -66,7 +66,7 @@ pre-commit run --all-files
 
 ## Dependency Update Policy
 
-The lockfile is updated automatically every Thursday at 08:00 UTC by the [`weekly-lockfile-update.yml`](.github/workflows/weekly-lockfile-update.yml) workflow, which runs `uv lock --upgrade` and opens a PR. GitHub Actions versions are updated monthly via [Dependabot](.github/dependabot.yml).
+See [DEPENDENCY_POLICY.md](DEPENDENCY_POLICY.md) for the full dependency update policy.
 
 When bumping a dependency version manually, update the constraint in `pyproject.toml` then run `uv lock --resolution lowest-direct` (see [RELEASE.md](RELEASE.md)).
 

DEPENDENCY_POLICY.md

@@ -0,0 +1,30 @@
+# Dependency Policy
+
+As a library consumed by downstream projects, the MCP Python SDK takes a conservative approach to dependency updates. Dependencies are kept stable unless there is a specific reason to update, such as a security vulnerability, a bug fix, or a need for new functionality.
+
+## Update Triggers
+
+Dependencies are updated when:
+
+- A **security vulnerability** is disclosed (via GitHub security alerts or PyPI advisories) in a dependency that directly affects the SDK's functionality or its consumers.
+- A bug in a dependency directly affects the SDK.
+- A new dependency feature is needed for SDK development.
+- A dependency drops support for a Python version the SDK still targets.
+
+Routine version bumps without a clear motivation are avoided to minimize churn for downstream consumers.
+
+## What We Don't Do
+
+The SDK does not run ad-hoc version bumps for PyPI dependencies. Updating a dependency can force downstream consumers to adopt that update transitively, which can be disruptive for projects with strict dependency policies.
+
+Dependencies are only updated when there is a concrete reason, not simply because a newer version is available.
+
+## Automated Tooling
+
+- **Lockfile refresh**: The lockfile is updated automatically every Thursday at 08:00 UTC by the [`weekly-lockfile-update.yml`](.github/workflows/weekly-lockfile-update.yml) workflow, which runs `uv lock --upgrade` and opens a PR. This does not alter the minimum or maximum versions for dependencies of the `mcp` package itself.
+- **GitHub security updates** are enabled at the repository level and automatically open pull requests for packages with known vulnerabilities. This is a GitHub repo setting, separate from the `dependabot.yml` configuration.
+- **GitHub Actions versions** are kept up to date via Dependabot on a monthly schedule (see `.github/dependabot.yml`).
+
+## Pinning and Ranges
+
+Production dependencies use compatible-release specifiers (`~=`) or lower-bound constraints (`>=`) to allow compatible updates. Exact versions are pinned only when necessary to work around a specific issue. The lockfile (`uv.lock`) records exact resolved versions for reproducible installs.

ROADMAP.md

@@ -0,0 +1,22 @@
+# Roadmap
+
+## Spec Implementation Tracking
+
+The SDK tracks implementation of MCP spec components via GitHub Projects, with a dedicated project board for each spec revision. For example, see the [2025-11-25 spec revision board](https://github.com/orgs/modelcontextprotocol/projects/26).
+
+## Current Focus Areas
+
+### Next Spec Revision
+
+The next MCP specification revision is being developed in the [protocol repository](https://github.com/modelcontextprotocol/modelcontextprotocol). Key areas expected in the next revision include extensions and stateless transports.
+
+The SDK has historically implemented spec changes promptly as they are finalized, with dedicated project boards tracking component-level progress for each revision.
+
+### v2
+
+A major version of the SDK is in active development, tracked via [GitHub Project](https://github.com/orgs/modelcontextprotocol/projects/31). Target milestones:
+
+- **Alpha**: ~mid-March 2026
+- **Beta**: ~May 2026
+
+The v2 release is planned to align with the next spec release, expected around mid-2026.

VERSIONING.md

@@ -0,0 +1,40 @@
+# Versioning Policy
+
+The MCP Python SDK (`mcp`) follows [Semantic Versioning 2.0.0](https://semver.org/).
+
+## Version Format
+
+`MAJOR.MINOR.PATCH`
+
+- **MAJOR**: Incremented for breaking changes (see below).
+- **MINOR**: Incremented for new features that are backward-compatible.
+- **PATCH**: Incremented for backward-compatible bug fixes.
+
+## What Constitutes a Breaking Change
+
+The following changes are considered breaking and require a major version bump:
+
+- Removing or renaming a public API export (class, function, type, or constant).
+- Changing the signature of a public function or method in a way that breaks existing callers (removing parameters, changing required/optional status, changing types).
+- Removing or renaming a public type or dataclass/TypedDict field.
+- Changing the behavior of an existing API in a way that breaks documented contracts.
+- Dropping support for a Python version that is still receiving security updates.
+- Removing support for a transport type.
+- Changes to the MCP protocol version that require client/server code changes.
+
+The following are **not** considered breaking:
+
+- Adding new optional parameters to existing functions.
+- Adding new exports, types, or classes.
+- Adding new optional fields to existing types.
+- Bug fixes that correct behavior to match documented intent.
+- Internal refactoring that does not affect the public API.
+- Adding support for new MCP spec features.
+- Changes to dev dependencies or build tooling.
+
+## How Breaking Changes Are Communicated
+
+1. **Changelog**: All breaking changes are documented in the GitHub release notes with migration instructions.
+2. **Deprecation**: When feasible, APIs are deprecated for at least one minor release before removal using `warnings.warn()` with `DeprecationWarning`, which surfaces warnings at runtime and through static analysis tooling.
+3. **Migration guide**: Major version releases include a migration guide describing what changed and how to update.
+4. **PR labels**: Pull requests containing breaking changes are labeled with `breaking change`.