New MCP spec drops sessions, easing AWS server deployments
The shift to stateless requests lets AWS deployments shed session-only infrastructure, but puts more focus on idempotent tool operations.
The latest MCP specification removes protocol-managed sessions, letting remote server requests go to any available instance and reducing the need for infrastructure dedicated to session handling. It also eliminates the initialization exchange and the Mcp-Session-Id header. Because stream resumption is no longer supported, clients may have to retry interrupted operations, making idempotency important for tools that cause side effects. Apify is adding stateless support alongside its sessionful server, while AWS recommends that gateways track protocol versions and keep legacy session infrastructure until older-client traffic has ended.
Why it matters
Removing protocol-managed sessions means MCP traffic can be handled by any available server instance, so operators can scale and balance requests without maintaining infrastructure whose only job is to keep protocol sessions alive. At the same time, losing stream resumability pushes more responsibility to clients, which may need to retry interrupted calls and ensure that tools causing side effects behave safely when invoked more than once. Providers like Apify and AWS are adapting by supporting both old and new protocol versions during the transition.
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Sources
- InfoQ