If you build MCP servers or clients, the next two months matter a lot. The MCP 2026-07-28 Release Candidate dropped on May 21 — the largest revision of the Model Context Protocol specification since launch — and the final spec ships July 28. That’s roughly a 10-week window to validate your implementations against breaking changes before the new standard locks in.

Here’s what’s changing, why it matters, and what you should be thinking about now.

The Headline: MCP Is Going Stateless

The single most impactful change in this RC is the elimination of the initialize handshake and session IDs. MCP is becoming a stateless protocol.

In the current protocol, every client-server interaction is bound to a session established by an initialize handshake. This means your infrastructure has to maintain session state somewhere — sticky sessions on your load balancer, a shared session store, or deep packet inspection at the gateway to route traffic to the right server instance. For anyone running MCP servers at any kind of scale, this has been an operational headache.

The RC removes all of that. A stateless MCP server can now run behind a plain round-robin load balancer. Traffic routes on an Mcp-Method header. Clients can cache tools/list responses for as long as the server’s ttlMs permits. The practical effect is that MCP servers become as simple to deploy and scale as ordinary REST APIs — no session state required.

The tradeoff is real: applications that need statefulness now own that state themselves, rather than relying on the protocol to carry it. But that’s a better design boundary. Stateless protocol, stateful applications — the spec handles the former; you handle the latter where you actually need it.

Server-to-Client Requests, Restructured

In the current protocol, servers can make requests back to clients (for things like sampling or showing progress). This pattern required an active session to work.

The RC restructures how server-to-client requests work to remain compatible with the stateless model. If you have MCP servers that actively push requests back to clients, this is a section of the RC you’ll want to read carefully — the mechanics change.

Extensions Become First-Class

The RC also formalizes the Extensions framework, giving it a proper home in the specification with reverse-DNS identifiers (e.g., io.modelcontextprotocol.tasks) to prevent naming collisions.

Two extensions graduate to official status:

MCP Apps — server-rendered user interfaces embedded within MCP. Think of it as the ability for an MCP server to serve a small interactive UI alongside its tools, without requiring a separate web application. The server controls the rendered interface; the client displays it.

Tasks — long-running work that outlives a single request-response cycle. If your MCP tool kicks off a background job that might take minutes or hours, Tasks gives you a standardized way to track and report on it rather than hacking together polling patterns.

Both have been in informal use; formalization means implementations can interoperate reliably.

Authorization Hardening

The RC tightens the OAuth 2.0 and OIDC implementation requirements. Key changes:

  • Issuer (iss) validation is now required — clients must verify the token issuer, closing a category of token substitution attacks
  • Refresh token support is standardized — consistent behavior across implementations
  • Token lifetime guidance tightened — the spec now provides clearer guidance on appropriate token lifetimes for MCP contexts

What’s Being Deprecated

Three features from the current spec are deprecated in the RC: Roots, Sampling, and Logging. These are still present but flagged for removal in a future version. If your implementation relies on any of these, now is the time to plan the migration path.

The RC also introduces a formal deprecation policy — a defined process for how the protocol will evolve and remove features going forward. This is a meaningful maturity signal: the protocol is growing up from “Anthropic’s internal tool” to “infrastructure standard,” and that requires a contract about backward compatibility.

Technical Additions: JSON Schema and Trace Context

Two additional standards get incorporated:

  • JSON Schema 2020-12 for tool definitions — more expressive schema for describing tool inputs and outputs
  • W3C Trace Context — standardized tracing headers, so MCP calls can participate in distributed tracing systems without custom instrumentation

For observability-focused teams, the trace context addition is particularly welcome. It means your MCP calls can flow through the same observability infrastructure as the rest of your stack.

The Timeline: You Have Until July 28

The RC is available now for developer validation. The final specification ships July 28, 2026. This RC contains breaking changes — statelessness, restructured server-to-client requests, the deprecations — so “I’ll deal with it after it ships” is a risky posture if you have production MCP servers.

The practical recommendation: run your MCP server implementation against the RC spec now. The initialize handshake and session ID removal will likely be the most impactful change to audit. Build a test client that speaks the stateless protocol and see what breaks.

The MCP ecosystem is growing fast — the shift to statelessness positions it to scale with that growth. The July 28 deadline is real; the work to get there starts now.

Sources

  1. Model Context Protocol Blog — The 2026-07-28 MCP Specification Release Candidate
  2. MCP Directory — RC Announcement Coverage
  3. MCP Playground Online — RC Analysis

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