MCP protocol versions

The Difference Between MCP Versions

Meandr takes each call in the revision your agent speaks and passes it to the server in the revision the server speaks.

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The problem

MCP's 2026-07-28 revision removed the handshake

Up to 2025-11-25, a client and a server agreed a version in the initialize handshake and held a session from there. 2026-07-28 has no initialize. A client built for 2025-11-25 or earlier opens with a handshake that a server speaking only 2026-07-28 does not recognise, and the connection never comes up.

Five revisions are in use. This is what each one changed.

Revision What changed
2024-11-05 The first spec. Transport is HTTP plus SSE, on two separate endpoints.
2025-03-26 Streamable HTTP replaces the two endpoints, and a session id header appears.
2025-06-18 Elicitation arrives — a tool can stop mid-call and ask the caller a question. JSON-RPC batching is removed.
2025-11-25 Elicitation gains a URL mode alongside the form.
2026-07-28 Stateless. No initialize, no session — every request carries its own version and capabilities.

The fix

Meandr translates between the agent's revision and the server's

You don't update the agent and you don't update the server. A 2025-06-18 client that a 2026-07-28 server would reject completes the call through Meandr.

  1. 01 How it works

    Each side keeps its own revision

    Your agent opens the connection naming the revision it was built for, and Meandr answers in that one. With the server, Meandr uses the newest revision the server supports, trying 2026-07-28 first.

    • Your agent keeps working in its own version, whether the server's is newer or older
    Agent 2025-06-18 Meandr MCP server 2026-07-28 v1 v2 v1 v2 v1 v2 v2 v1 v2 v1 v2 v1

  2. 02 Add a server

    Meandr detects the revision after you add the server

    You fill in the endpoint, name, transport and authentication. As soon as the server is added, Meandr connects to it and identifies its protocol version automatically.

  3. 03 See it

    See the version in the Server catalog window

    Once you add the server, the Server catalog window opens. It shows the MCP protocol version the server uses, next to its name.

Questions about MCP protocol versions

What if a server speaks a revision Meandr doesn't support?
You find out when you add it, not mid-call. Meandr reads the revision the moment you connect a server. If there is no revision in common, the server shows as failed in the dashboard, with a retry button, and its tools are never imported.
Do approvals still work on 2026-07-28?
Yes, by a different route. On 2026-07-28 nothing can hold the connection open while a person decides. Meandr answers with the approval request instead, and your agent asks again once someone has decided.
What happens when a server upgrades?
Nothing on your side. Meandr checks every server again each hour, so a move from 2025-06-18 to 2026-07-28 shows in the dashboard within the hour. Your agent keeps the one it has.
Does an older agent lose anything against a newer server?
Nothing. Tool calls, approvals and questions the server asks during a call all keep working. The server's questions reach your agent in a form it understands, and if it can't show them, someone answers in the dashboard.
Does version translation need an extra component?
No. Your agents keep pointing at the same Meandr endpoint, over standard MCP — Streamable HTTP or SSE. Nothing extra to deploy, nothing to keep patched.

Add a server without checking its revision first

Run any MCP server in Meandr or connect the ones you already have, then point every agent at one MCP gateway. Policy, approvals and audit cover every call, with no code changes.

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