MCP Goes Stateless and Kills the Initialize Handshake. Six Breaking Changes Lock July 28.

Ten days. That's the window.

The MCP 2026-07-28 release candidate drops the initialize/initialized handshake entirely. Protocol version, client info, and capabilities now ride in _meta on every request, with a new server/discover method if you want to fetch capabilities upfront. Six breaking changes total, locking on the 28th.

The statelessness change is the one with real architectural consequences. Remote MCP servers currently need sticky sessions and a shared session store, which means you're running Redis or equivalent just to keep an agent conversation on the same box. Post-RC, servers can sit behind plain round-robin load balancers and route on an Mcp-Method header. That deletes an entire class of deployment complexity. If you've been putting off shipping a remote MCP endpoint because the session-affinity plumbing looked annoying, the reason just evaporated.

Authorization hardens to OAuth 2.1 with mandatory Protected Resource Metadata. Tasks graduates out of experimental. MCP Apps ships sandboxed-iframe HTML UIs, which is the first real answer to "how does an MCP tool render something richer than text." And there's a new lifecycle policy guaranteeing a 12-month minimum Active → Deprecated → Removed window, which is the spec authors acknowledging they've been churning faster than implementers can track.

Put this story next to the audit above and the picture gets uncomfortable. The protocol is hardening. Mandatory PRM, sandboxed UI, explicit deprecation windows. That's a spec growing up. The server ecosystem built on it is 23% exploitable and nobody can tell which 23% from the outside. Spec maturity and ecosystem maturity are diverging, and the spec is the part that gets the press releases.

For builders: if you maintain an MCP server, read the RC this weekend. Ten days isn't much and the handshake removal is not a mechanical find-and-replace. If you consume MCP servers, your clients will handle the transition, but expect a rough two weeks after the 28th as maintainers catch up. Pin versions if you have anything running unattended.

Worth noting alongside this: AWS published how Smartsheet built its production remote MCP server, covering auth, multi-tenancy, governance, and scaling. Real reference architectures for remote MCP are still rare. Most public MCP content is a local stdio toy that reads three files. This one's worth the read even though it predates the RC.