MCP new specs in Practice: Testing the Stateless Revolution on AWS AgentCore Gateway

Short summary

The Model Context Protocol published its most significant revision on July 28, 2026, making MCP fully stateless with seven breaking changes including elimination of session handshakes, HTTP-native routing headers, cache metadata, and OAuth 2.0 alignment. The author tested the new spec against AWS AgentCore Gateway with real Lambda tools, providing before/after wire examples and practical takeaways. Roots, Sampling, and Logging features enter a 12-month deprecation window ending mid-2027.

• •MCP 7-28 introduces seven breaking changes: stateless protocol, HTTP-native routing, cache metadata, MRTR replacing SSE, OAuth 2.0 hardening, cleaner errors, and JSON Schema 2020-12
• •Author tested the spec against AWS AgentCore Gateway with real Lambda tools and provides wire-level before/after examples
• •Roots, Sampling, and Logging are deprecated with a 12-month migration window until mid-2027

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