AWS: MCP specification makes protocol stateless and drops session affinity
The updated Model Context Protocol (MCP) specification removes the initialize/initialized handshake and the Mcp-Session-Id header, allowing requests to be routed independently to any server instance and eliminating the protocol-level requirement for sticky sessions or shared session stores. AWS maps the change to its Well-Architected Agentic AI guidance, highlights serverless and conventional load-balancer deployment patterns, notes new headers and tracing/caching controls (Mcp-Method, Mcp-Name, W3C Trace Context, ttlMs, cacheScope), and warns that clients must handle retries and idempotency because stream resumability was removed.