Fixed (verified)Last checked Oct 17, 2026MCP#transport #config

Streamable HTTP client overwrites a custom Accept header

A custom Accept header set in requestInit.headers is replaced by the SDK default, breaking endpoints that need a specific value.

From GitHub

modelcontextprotocol/typescript-sdk

Issue Pull request

Difficulty: Easy
Time: ~5 min
Steps: 1
Fixed in: @modelcontextprotocol/client@2.0.0
Last checked: Oct 17, 2026

Verified fix: PR #1655 merged on 2026-04-02. Fixed in @modelcontextprotocol/client@2.0.0 (first stable release containing the merge commit). Last checked 2026-10-17.

Symptom

A custom Accept header set in requestInit.headers is replaced by the SDK default, breaking endpoints that need a specific value.

Evidence what you'll see

Reported on @modelcontextprotocol/sdk 1.17.4
The server sees the default Accept header, not yours

Cause

StreamableHTTPClientTransport always set its own Accept header, ignoring one already supplied.

Fix steps

0 of 1 done

Step 1Upgrade to a client release that includes PR #1655, which only sets the default Accept header when you haven't provided one.

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Verify the fix worked

Inspect the outgoing request and confirm your Accept header is sent.

Sources and credit

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