MCP Python SDK v2.0.0b2 adds client-side subscriptions and httpx2

The Model Context Protocol (MCP) Python SDK released version 2.0.0b2, introducing client-side subscription support and replacing the HTTP stack with httpx2.

• The SDK replaces httpx and httpx-sse with httpx2 (>2.5.0), updating TLS verification to use the OS trust store and renaming loggers.
• Client-side subscriptions/listen (SEP-2575) are now available via a context manager that waits for server acknowledgment before yielding events.
• Request cancellation now functions correctly on 2026 transports by closing the POST/SSE stream or sending notifications/cancelled over stdio.
• Resolver dependency injection has been extended to support Sample and ListRoots requests in addition to Elicit.

This pre-release allows developers to test new protocol features ahead of the stable v2 target for 2026-07-28.