MCP's Final Spec Is Live — Claude Support Comes Later

The Model Context Protocol's 2026-07-28 specification became final on July 28, 2026, and it goes further than the release candidate suggested: Roots, Sampling and Logging are now formally deprecated, replaced by a new Multi Round-Trip Requests (MRTR) pattern. Anthropic published its own rollout post the same day — but Claude only supports part of the new spec today; the stateless core and full OAuth alignment are still "rolling out soon," in Anthropic's own words.

What the final spec adds beyond the RC

CodingSalt covered the stateless core, MCP Apps and Tasks extension when the release candidate locked in May. The final text, published July 28, adds several changes that were not settled at RC stage:

• Roots, Sampling and Logging are deprecated (SEP-2577). These features still work during the transition window, but new servers should pass files or directories through tool parameters instead of Roots, call an LLM provider's API directly instead of Sampling, and log to stderr or OpenTelemetry instead of the Logging capability.
• Multi Round-Trip Requests (MRTR) (SEP-2322) replaces the server-initiated calls those three features relied on. Every result now carries a required resultType field — "complete" for a normal answer or "input_required" when the server needs more from the client.
• server/discover becomes a mandatory RPC so a server can advertise its supported protocol versions and capabilities up front, letting clients pick a version before sending real requests.
• subscriptions/listen replaces the old HTTP GET endpoint plus resources/subscribe/unsubscribe pair with one long-lived stream that clients opt into per notification type.
• OAuth Dynamic Client Registration is deprecated in favor of Client ID Metadata Documents, and authorization responses must carry an iss parameter per RFC 9207 to close a token-redemption ambiguity.

MRTR in practice

A server that used to call sampling/createMessage mid-tool-call now returns an interim result instead of reaching back into the client:

{
  "resultType": "input_required",
  "inputRequests": [
    { "type": "sampling", "prompt": "Summarize this diff for a commit message" }
  ]
}

The client fills in inputResponses and re-sends the original request — there is no separate completion notification to correlate, which is also why the spec removes notifications/elicitation/complete from the previous revision. Any server code built around a fire-and-forget callback from the client needs to be rewritten around this retry loop.

What Claude actually supports on day one

This is the gap developers building specifically for Claude should plan around. Per Anthropic's own rollout post, Claude currently supports:

• MCP Apps (interactive UI rendered inside conversations)
• Enterprise-managed authorization for organization-wide connector provisioning
• A connector observability dashboard
• A research-preview private network tunnel for connectors without public endpoints
• A connectors directory listing more than 950 MCP servers

The stateless protocol core, the formal extensions framework, and full OAuth 2.0/OIDC alignment are explicitly not on that list yet — Anthropic describes them as rolling out "soon" rather than shipped. If your server targets Claude specifically, the session-based transport you have today still works; if it targets the broader MCP ecosystem, plan for clients that pick up the stateless core faster than Claude does.

Adoption context

Anthropic's post cites 400 million monthly SDK downloads for MCP, a 4x increase over the past year, and describes millions of daily Claude users touching connectors. Beyond Anthropic, the protocol blog lists AWS integrating the stateless core into Bedrock AgentCore and making Tasks an official extension, Microsoft integrating it into Foundry, and Google Cloud committing to adopt it "across our ecosystem of developer tools." Figma, Intuit, Netlify, PostHog, Xero and Zoom are named as supporting the new spec as well.

What to do this week

1. Grep your server for Roots, Sampling or Logging usage. None of it breaks today, but the 12-month deprecation clock started July 28.
2. Don't rewrite for MRTR yet if you only target Claude. Claude's own core support is still pending; watch the Claude changelog before ripping out session-based code that currently works.
3. If you serve multiple clients, prioritize server/discover. It is the one addition every client, regardless of vendor, can use immediately for version negotiation.
4. Re-check OAuth client registration. If your authorization server relies on Dynamic Client Registration, start evaluating Client ID Metadata Documents now — it is a deprecation, not a hard break, but a 12-month window disappears fast for infrastructure teams.