Transports changedspecification/2025-06-18/basic/transports
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4848> [!NOTE]
4949>
5050> This replaces the [HTTP+SSE
51> transport](/specification/2024-11-05/basic/transports#http-with-sse) from
51> transport](/specification/2024-11-05/basic/transports.md#http-with-sse) from
5252> protocol version 2024-11-05. See the [backwards compatibility](#backwards-compatibility)
5353> guide below.
5454
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164164### Session Management
165165
166166An MCP "session" consists of logically related interactions between a client and a
167server, beginning with the [initialization phase](/specification/2025-06-18/basic/lifecycle). To support
167server, beginning with the [initialization phase](/specification/2025-06-18/basic/lifecycle.md). To support
168168servers which want to establish stateful sessions:
169169
1701701. A server using the Streamable HTTP transport **MAY** assign a session ID at
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239239For example: `MCP-Protocol-Version: 2025-06-18`
240240
241241The protocol version sent by the client **SHOULD** be the one [negotiated during
242initialization](/specification/2025-06-18/basic/lifecycle#version-negotiation).
242initialization](/specification/2025-06-18/basic/lifecycle.md#version-negotiation).
243243
244244For backwards compatibility, if the server does *not* receive an `MCP-Protocol-Version`
245245header, and has no other way to identify the version - for example, by relying on the
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252252### Backwards Compatibility
253253
254254Clients and servers can maintain backwards compatibility with the deprecated [HTTP+SSE
255transport](/specification/2024-11-05/basic/transports#http-with-sse) (from
255transport](/specification/2024-11-05/basic/transports.md#http-with-sse) (from
256256protocol version 2024-11-05) as follows:
257257
258258**Servers** wanting to support older clients should:
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