What is the MCP SSE transport?
SSE was MCP's first remote transport. The spec replaced it with Streamable HTTP in version 2025-03-26.
The SSE transport is the original way a remote MCP server talked to an app, defined in MCP spec 2024-11-05. Spec 2025-03-26 replaced it with Streamable HTTP. Newer servers use that instead.
Also called MCP SSE, HTTP+SSE, HTTP with SSE, MCP SSE server, server-sent events MCP.
The 2024-11-05 spec listed two standard transports: stdio for local servers and HTTP with SSE for remote ones. The SSE version needed two endpoints: one to open a stream and one for the app to post messages.
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The 2025-03-26 spec introduced Streamable HTTP and said it replaces the HTTP+SSE transport from 2024-11-05. It calls the old transport deprecated and explains how apps and servers can stay compatible with it.
SSE (Server-Sent Events) was not dropped entirely. Streamable HTTP can still use it to stream replies. In the latest spec, 2026-07-28, a reply arrives as a JSON object or a request-scoped SSE stream.
Related:Streamable HTTPRemote MCP serverLocal MCP serverMCP serverModel Context Protocol (MCP)
The MCP SSE transport is the old way a remote server talked to your app, and the spec replaced it with Streamable HTTP in version 2025-03-26. If a server offers only an SSE endpoint, it uses the old method. The one thing to know first: your app may still connect to it.
Claude Code marks SSE as deprecated and says to use HTTP servers where available. It tries the HTTP method first and switches to SSE if the server does not accept it. That automatic switch needs Claude Code v2.1.265 or later. On an earlier version, you pass --transport sse yourself when you add the server.
Our advice: if you build a server, use Streamable HTTP for remote servers and stdio for local ones, and do not start a new server on SSE.
Good for
- People whose server address ends in /sse
- Claude Code users adding an older remote server
- Builders choosing how to serve a new MCP server
Comparison
Our advice: use Streamable HTTP for any hosted server. HTTP+SSE only matters if you must connect to an older server.
| Option | Runs | In the spec | Status |
|---|---|---|---|
| stdio | Local | 2024-11-05 | Standard |
| HTTP+SSE | Hosted | 2024-11-05 | Replaced |
| Streamable HTTPThis page | Hosted | 2025-03-26 | Standard |
Often compared with
1
- Streamable HTTP transport
Questions
What is the MCP SSE transport?
The first way a remote MCP server talked to an app, from spec version 2024-11-05. It used a stream for server messages and a separate web address for the app's messages.
Is MCP SSE deprecated?
Yes. Spec 2025-03-26 replaced HTTP+SSE with Streamable HTTP and calls the old transport deprecated. Claude Code also marks SSE as deprecated.
What is the difference between SSE and Streamable HTTP?
The old SSE method needed two web addresses. Streamable HTTP uses one. Each message is an HTTP POST to that address, and the reply comes back as plain JSON or as a stream.
Does Streamable HTTP still use SSE?
Optionally. The server can stream its reply with Server-Sent Events. The difference is that SSE is now a way to send a reply, not a separate connection you set up first.
My server address ends in /sse. Will it work in Claude Code?
It can. Claude Code v2.1.265 or later tries the HTTP transport first and switches to SSE if the server does not accept it. On an earlier version, add it with claude mcp add --transport sse <name> <url>. Ask the vendor for a Streamable HTTP address if there is one.
Should I build a new MCP server with SSE?
Our advice: no. The spec replaced it with Streamable HTTP, and Claude Code says to use HTTP servers instead where available. Use Streamable HTTP for remote servers and stdio for local ones, and keep old SSE endpoints only if you must support older apps.
What spec version replaced SSE?
2025-03-26. The latest spec, 2026-07-28, lists stdio and Streamable HTTP as its standard transports.
Is MCP SSE the same as the SSE in browsers?
It builds on the same web feature, Server-Sent Events, which lets a server push a stream of messages over HTTP. MCP defines how it is used for its own messages.
Sources
Docs, issue trackers and discussions this page is built from.
Show all 5Hide
- Transports (2025-03-26) · modelcontextprotocol.io
- Transports (2024-11-05) · modelcontextprotocol.io
- Transports · modelcontextprotocol.io
- Connect Claude Code to tools via MCP · code.claude.com
- Architecture overview · modelcontextprotocol.io