---
title: MCP Replaces initialize Handshake With _meta Fields
description: The 2026-07-28 MCP spec removes the initialize handshake. Every request now carries protocol version and capabilities in _meta fields instead.
date: 2026-08-06T00:00:00.000Z
category: ai-productivity
tags: mcp, model-context-protocol, agents, api
---

## Quick Answer

The MCP 2026-07-28 specification [removes the `initialize`/`notifications/initialized` handshake](https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning) entirely. Protocol version and client capabilities now travel in every request's `_meta` field (`io.modelcontextprotocol/protocolVersion`, `io.modelcontextprotocol/clientCapabilities`), not negotiated once at connection start. A client or server built around "negotiate once, trust it for the session" needs to move that negotiation into per-request `_meta` handling instead.

## What's actually changing

The specification changelog states it directly:

> "Removed `initialize`/`notifications/initialized` handshake; requests now carry protocol version and capabilities in `_meta` (`io.modelcontextprotocol/protocolVersion`, `io.modelcontextprotocol/clientCapabilities`); version mismatches return `UnsupportedProtocolVersionError`"

This follows directly from [the removal of protocol-level sessions](/ai-productivity/mcp-removes-protocol-level-sessions/): if there's no persistent session, there's no connection-scoped handshake result to hold onto either. Every request has to be self-describing.

A real request under the new shape:

```json title="tools/call request with protocol version and capabilities in _meta"
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "search",
    "arguments": { "query": "stateless MCP" },
    "_meta": {
      "io.modelcontextprotocol/protocolVersion": "2026-07-28",
      "io.modelcontextprotocol/clientInfo": {
        "name": "example-client",
        "version": "1.0.0"
      },
      "io.modelcontextprotocol/clientCapabilities": {
        "extensions": {}
      }
    }
  }
}
```

## Structural Comparison Matrix

| Operational Aspect                  | Before (initialize handshake)            | After (2026-07-28+)                                                                   |
| :---------------------------------- | :--------------------------------------- | :------------------------------------------------------------------------------------ |
| **When negotiation happens**        | Once, at connection start                | Every request                                                                         |
| **Where version/capabilities live** | Handshake response, held for the session | `_meta.io.modelcontextprotocol/protocolVersion` and `clientCapabilities` on each call |
| **Version mismatch behavior**       | Handshake failure                        | `UnsupportedProtocolVersionError`, listing supported revisions                        |

## Fix it: move negotiation into per-request \_meta

<Callout
  type="warning"
  title="Handle UnsupportedProtocolVersionError explicitly"
>
  Since the server's error response lists the revisions it actually supports, a
  client should retry with a mutually supported version rather than treating any
  mismatch as a hard failure. Skipping that retry logic means a client that only
  speaks an older revision fails outright against a server that could have
  served it a compatible version.
</Callout>

Any code that previously stored a "session established" flag after a successful `initialize` call, then skipped re-sending capabilities on later calls, needs that flag and the associated shortcut removed. Every outgoing request needs the `_meta` block populated fresh, not conditionally based on connection state that no longer exists.

## Confirmed version

Sourced from the official Model Context Protocol specification changelog, 2026-07-28 revision, published 2026-07-28, including the real example request shape from the spec's own migration documentation. Browse more posts like this in the [AI Productivity](/ai-productivity) archive.