MCP Goes Stateless in Biggest Spec Rewrite as A2A Joins AAIF

A protocol rebuilt around how the web already works

The Model Context Protocol has been rebuilt from the ground up. The 2026-07-28 specification, released on July 28, turns MCP from a two-way protocol that held a connection open into a stateless request/response protocol. Updated TypeScript, Python, Go and C# SDKs shipped on the same day2. The maintainers call the stateless core the release's headline feature, and say it was one of the changes developers asked for most because they wanted servers that were more reliable and easier to scale2.

Cloudflare welcomed the release under the banner "the next generation of MCP" and was blunt about what had been wrong. The protocol started out with a local STDIO transport, and when servers moved onto the web they brought that connection model with them. That forced operators to deal with sticky sessions, held-open streams and message replay1. Cloudflare's view is that this overhead is now gone, and that an MCP server can run as a single Worker without any stateful infrastructure behind it1.

The timing matters. A few weeks after the release, Google's Agent2Agent (A2A) protocol joined the Agentic AI Foundation (AAIF), the Linux Foundation body that already hosts MCP15. Taken together, the two events suggest that agent infrastructure is settling into an open, vendor-neutral stack. MCP connects an agent to tools and data. A2A lets agents talk to each other.

What actually changed in MCP

All the technical coverage agrees on the core change. The initialize/initialized handshake is gone, and so is the Mcp-Session-Id header. Every request now carries its own protocol version, client identity and capabilities in a _meta field. In practice, any request can be sent to any server instance behind an ordinary round-robin load balancer, with no shared storage28. The AAIF's own explainer adds that operators can now scale horizontally and swap server instances in and out without keeping session state in sync3.

The maintainers make clear that this doesn't make applications stateless. A server that needs to remember something between calls can issue an explicit handle from a tool, and the model passes it back as an argument. The maintainers argue this works better than state hidden in the transport, because the model can see the handle2.

Multi Round-Trip Requests (MRTR) replace the server-initiated calls that used to need an open stream, such as elicitation and sampling. A server returns an input_required result, and the client retries the original call with the answers attached2. Cloudflare admits this breaks the old elicitation flow but argues it is far easier to run in production1. Supabase's reaction shows why. Its stateless MCP server couldn't easily support elicitation before. With MRTR it can now ask a user to confirm something like a new project's cost, or a query that would delete data, before acting2.

The other changes are aimed at operations teams. Streamable HTTP requests must now carry Mcp-Method and Mcp-Name headers, so gateways, rate limiters and web application firewalls can make decisions from headers without parsing JSON bodies2. List responses now include ttlMs and cacheScope hints, and tool catalogs come back in a fixed order, which keeps upstream prompt caches stable1.

Authorization and governance

The security changes are less visible but probably matter more to large companies. Client credentials are now tied to the issuer that created them, RFC 9207 issuer validation is adopted, and Dynamic Client Registration (DCR) is formally deprecated in favor of Client ID Metadata Documents (CIMD)2. Cloudflare reports that DCR is scheduled for removal after summer 20271. Praesidia notes that OAuth 2.1 is still the foundation. This release tightens it rather than replacing it8.

The release also adds a formal feature lifecycle. A deprecated feature must stay available for at least 12 months before it can be removed. Roots, Sampling, Logging, DCR and the legacy HTTP+SSE transport are all deprecated in this release1. Tasks, MCP Apps and Enterprise-Managed Authorization now sit in a versioned extensions framework rather than the core protocol8. That keeps a tools-only server simple while letting others opt into advanced features3.

The lifecycle policy may matter more than any single wire-level change. A deprecation window is a promise to anyone budgeting a multi-year platform, and it is the kind of commitment enterprise buyers usually ask for before they standardize on something.

The enterprise endorsement wall

The official announcement includes a long list of supporting quotes. AWS says the stateless core is available in Amazon Bedrock AgentCore and that it contributed Tasks for long-running agents. Microsoft calls MCP foundational to Foundry. Google Cloud describes the release as a big step for enterprise AI scalability2. Honeycomb says agents now make close to 20% of its monthly interactive queries. Manufact reports that its package is about 83% smaller and 25% faster after the SDK client-server split2.

There are early production stories too. Sentry co-founder David Cramer said his team went live on the new protocol before the spec was finalized without breaking production1. Cloudflare says its Code Mode MCP server has handled billions of tool calls using an earlier unofficial stateless mode1. Anthropic's David Soria Parra, MCP's co-creator, called it the most significant advance since launch1.

These are vendor statements, and they come from companies that benefit if MCP is adopted. Still, the agreement is broad. It covers rival clouds, developer tool companies and governance startups, and that suggests the stateless redesign fixed a real, shared pain point rather than one company's preference.

A2A completes the picture

On the agent-to-agent side, A2A was announced by Google in April 2025, donated to the Linux Foundation in June 2025, and reached its stable v1.0 release in March 202618. v1.0 added Signed Agent Cards for cryptographic identity, multi-tenancy and version negotiation16. At its first anniversary, the Linux Foundation counted more than 150 supporting organizations. It also reported A2A integrations in Azure AI Foundry, Copilot Studio and Amazon Bedrock AgentCore Runtime, along with production use in supply chain, financial services, insurance and IT operations13.

The Linux Foundation describes the two protocols as complementary. A2A handles coordination between agents, including across organizations, while MCP connects agents to tools and data13. With A2A joining AAIF, both now sit alongside Block's goose, OpenAI's AGENTS.md and the agentgateway proxy15.

Forbes adds a useful caveat. Google gave A2A to neutral governance more than a year ago, so the AAIF move settles where it is hosted, not who controls it15. The same analysis notes that the transfer doesn't standardize enterprise authorization policy, which is still a gap15.

Where the reporting diverges

Several details differ between outlets, and readers should treat the figures with caution. Most sources date A2A's move into AAIF to August 171518, while Enterprise DNA gives August 2017. Agora Intelligence ties A2A v1.0 to April 9, 202620, but other timelines place v1.0 in March and April 9 at the anniversary announcement18. Eco's explainer says A2A went into AAIF in 202521, which conflicts with most other accounts.

The numbers for AAIF and MCP adoption also vary. One outlet says AAIF had fewer than 40 members at its December 2025 launch and more than 250 by August 202618. Another says it started with 49 founding members in March 202617. For MCP, some secondary sources still quote about 97 million monthly SDK downloads18, while the maintainers now report close to half a billion monthly downloads across Tier 1 SDKs2. Forbes points out that the A2A adoption figures come from the foundation and vendors rather than independent measurement15, and that warning fits nearly every number in this story.

One technical detail is also disputed. One developer guide says server/discover is required12. Cloudflare and the AAIF explainer describe it as optional for clients that want to check a server's capabilities first13. Implementers should check the specification text itself rather than secondary summaries.

Our reading: plumbing is becoming boring

We read the stateless rewrite as MCP accepting that it is a web protocol, with everything that implies about operations. The interesting work in enterprise AI agents is moving from "can the agent call the tool" to questions about governance, identity and audit. That fits the security pressure on the protocol. In May 2026, the NSA's Artificial Intelligence Security Center called MCP flexible but underspecified, pointing to serialization risks, trust boundaries and agent misuse11. Tighter authorization and gateway-friendly headers respond directly to that kind of criticism, though they don't close every gap.

The cost is migration. The change breaks compatibility, and servers that depend on sessions or server-initiated requests will need a deliberate transition1. Teams can plan for it with the 12-month deprecation floor, a standardized tool layer in MCP, an agent-coordination layer in A2A, and both governed by one neutral foundation. Cramer's summary fits: agents only become useful once the plumbing stops being the main story1.