The 2026-07-28 MCP spec is the biggest revision since the protocol launched, and it is not backward compatible. The release candidate locked on May 21, 2026, and the spec ratifies July 28. If you run a production Model Context Protocol server, some of your code stops working that day.
Most of the write-ups so far explain the why (MCP went stateless, here is what that means for scaling). That part is genuinely interesting. But if you maintain a server, the question you actually have is narrower: which lines in my code break, and what do I change them to. This post is that list. Seven changes, each with the before/after and a grep you can run right now.
I am citing SEP numbers throughout so you can read the source proposals yourself. Don't take my word for any of it.
1. The session is gone (SEP-2567)
This is the headline change. The Mcp-Session-Id header and the protocol-level session it created are removed. The 2026-07-28 transport is stateless: any request can land on any server instance.
