Confusion about “Streamable HTTP” in MCP — is HTTP/2 actually required for the new bidirectional streaming?

[frosk1]

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Discussion Topic

Hey folks,
I’ve been digging into the new “Streamable HTTP” transport introduced for MCP (Model Context Protocol) — replacing the old HTTP + SSE setup — and I’m trying to confirm one specific point that seems strangely undocumented:

👉 Is HTTP/2 (or HTTP/3) actually required for Streamable HTTP to work properly?

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What I found so far:

The official MCP spec and Anthropic / Claude MCP blogs (and Cloudflare’s “Streamable HTTP MCP servers” post) all describe the new unified single-endpoint model where both client and server send JSON-RPC messages concurrently.

That clearly implies full-duplex bidirectional streaming, which HTTP/1.1 simply can’t do — it only allows server-to-client streaming (chunked or SSE), not client-to-server while reading.

In practice, Python’s fastmcp and official MCP SDK use Starlette/ASGI apps that work fine on Hypercorn with --h2, but will degrade on Uvicorn (HTTP/1.1) to synchronous request/response mode.

Similarly, I’ve seen Java frameworks (Spring AI / Micronaut MCP) add “Streamable HTTP” server configs but none explicitly say “requires HTTP/2”.

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What’s missing:

No documentation — neither in the official spec, FastMCP, nor Anthropic’s developer docs — explicitly states that HTTP/2 or HTTP/3 is required for proper Streamable HTTP behavior.

It’s obvious if you understand HTTP semantics, but confusing for developers who spin up a simple REST-style MCP server on Uvicorn/Flask/Express and wonder why “streaming” doesn’t stream or blocks mid-request.

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What I’d love clarity on:

1. Is there any official source (spec, SDK doc, blog, comment) that explicitly says Streamable HTTP requires HTTP/2 or higher?

2. Have you successfully run MCP clients and servers over HTTP/1.1 and observed partial streaming actually work? I guess not...

3. In which language SDKs (Python, TypeScript, Java, Go, etc.) have you seen this acknowledged or configured (e.g. Hypercorn --h2, Jetty, HTTP/2-enabled Node, etc.)?

4. Why hasn’t this been clearly documented yet? Everyone migrating from SSE to Streamable HTTP is bound to hit this confusion.

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If anyone from Anthropic, Cloudflare, or framework maintainers (fastmcp, modelcontextprotocol/python-sdk, Spring AI, etc.) sees this — please confirm officially whether HTTP/2 is a hard requirement for Streamable HTTP and update docs accordingly 🙏

Right now there’s a huge mismatch between the spec narrative (“bidirectional JSON-RPC on one endpoint”) and the ecosystem examples (which silently assume HTTP/2).

Thanks in advance for any pointers, example setups, or authoritative quotes!

[frosk1]

Answered in reddit thread:

https://www.reddit.com/r/mcp/s/XPaRnyxlD3

Though the request still stands, why not using http2 for async dublex multi direction streaming?