# MCP 2026-07-28 Goes Stateless: What Breaks and How to Migrate > Source: > Published: 2026-08-09 12:21:01+00:00 MCP just killed its session model. The **2026-07-28 specification** — the biggest protocol revision since MCP launched in 2024 — removes the stateful handshake, drops session IDs, and makes every request self-contained. If you have an MCP server in production, some of your code will break. Here is exactly what changed, what stops working, and how to migrate. ## The Handshake Is Dead The old model required an `initialize/notifications/initialized` exchange before any real work could happen. That handshake established a session, and the `Mcp-Session-Id` header bound all subsequent requests to the same server instance. It was a reasonable design for a protocol still living on localhost. It was a terrible design for anything running at scale. The [official 2026-07-28 changelog](https://modelcontextprotocol.io/specification/2026-07-28/changelog) removes all of it. Every request now carries protocol version, client info, and capabilities in a `_meta` field inline. No handshake, no session header, no server instance affinity. There is an optional `server/discover` call for capability negotiation upfront — but it is optional, not a prerequisite. Servers that stored cross-call state keyed to a session ID need to rethink their approach. The new spec (SEP-2567) is explicit: servers mint opaque handles and pass them as ordinary tool arguments. State becomes opt-in and visible, not implicit and hidden in a session layer. ## Server-to-Client Requests, Redesigned Sampling, elicitation, and roots discovery used to require an open bidirectional stream — the main reason MCP servers had to maintain persistent connections. The 2026-07-28 spec replaces this with **Multi Round-Trip Requests (MRTR)**. When a tool call needs something from the client mid-execution — an LLM completion, user input, a roots list — the server returns an `InputRequiredResult` instead of completing. This result carries `inputRequests` (what the server needs) and an opaque `requestState` the client must echo back. The client re-issues the original call with `inputResponses` and the echoed state. Any server instance can resume. No session affinity needed. The features developers most relied on persistent connections for — sampling, elicitation — now work over plain stateless HTTP. The operational workarounds required to deploy these in production are gone. ## What Actually Breaks in Your Server Here is the concrete list of what needs to change in an existing MCP server: **Initialization gates**— Logic that waits for the handshake to complete before processing requests. Remove it: the handshake does not exist.** Session-keyed state**— Any cross-call state keyed to`Mcp-Session-Id` . Rewrite to use server-minted handles passed as tool arguments.**Sticky session configuration**— Load balancer rules pinning sessions to specific instances. No longer needed.** SSE transport dependencies**— HTTP+SSE is now formally deprecated. Migrate to Streamable HTTP. The [Python SDK v2 migration guide](https://github.com/modelcontextprotocol/python-sdk) is the most involved — maintainers describe it as a “major rework.” TypeScript, Go, and C# also have v2 releases with dedicated migration documentation. All four ship 2026-07-28 support as of release day. ## What You Gain Running a remote MCP server before 2026-07-28 meant sticky session affinity at the load balancer (which kills autoscaling), a shared session store for horizontal scale, and often deep packet inspection at the gateway to route on session IDs. The operational overhead was real and expensive. After the update: a plain round-robin load balancer is sufficient. `Mcp-Method` and `Mcp-Name` HTTP headers let gateways route and authorize without touching the request body. Serverless deployments on Lambda, Cloudflare Workers, or Vercel Edge work without modification. [AWS AgentCore Gateway](https://aws.amazon.com/blogs/machine-learning/how-agentcore-gateway-supports-the-mcp-2026-07-28-spec/), Microsoft App Service, and Google Cloud all confirmed 2026-07-28 support on release day. Tool catalog caching (SEP-2549) is a quieter improvement with real cost impact. `tools/list` and `prompts/list` responses now carry `ttlMs` and `cacheScope` fields. Clients cache the tool catalog across reconnects, which keeps upstream LLM prompt caches stable and cuts inference costs on reconnect-heavy workloads. ## The Grace Period A v2 server answers the legacy `initialize` handshake alongside `server/discover` , so existing clients on the 2025-11-25 spec keep connecting without changes. You can upgrade servers first and migrate clients separately. Roots, Sampling, and Logging are deprecated, not removed. The HTTP+SSE transport is deprecated. The deprecation policy guarantees a minimum 12-month window — nothing disappears before July 2027. That is a reasonable runway given the size of the change. Per the [official MCP announcement](https://blog.modelcontextprotocol.io/posts/2026-07-28/), 97 million monthly SDK downloads are in scope for this migration. The stakes of a botched rollout are real. The backward compatibility bridge and the 12-month window exist for exactly this reason. Start migrating now, while the runway is long.