# MCP 2026-07-28 specification

Mastra's @mastra/mcp 2.0 now supports the MCP 2026-07-28 specification, which removes server sessions so every request is self-contained. Under the previous spec a client opened each connection with an initialize request, the server returned a session ID, and later requests had to carry it; a load balancer routing to another instance produced 400 session not found errors, worked around with sticky sessions or a shared store such as Redis. Now any instance can answer any request, a round-robin balancer suffices, and if an instance crashes the next request goes elsewhere while the client continues.

Mastra's @mastra/mcp 2.0 now supports the MCP 2026-07-28 specification, which removes server sessions so every request is self-contained. Under the previous spec a client opened each connection with an initialize request, the server returned a session ID, and later requests had to carry it; a load balancer routing to another instance produced 400 session not found errors, worked around with sticky sessions or a shared store such as Redis. Now any instance can answer any request, a round-robin balancer suffices, and if an instance crashes the next request goes elsewhere while the client continues.