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fix: add Transfer-Encoding chunked to SSE responses #1723

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fix: add Transfer-Encoding chunked to SSE responses #1723

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6b503c9
fix: add Transfer-Encoding chunked to SSE responses (#1619)
guoyangzhen Mar 20, 2026
73389b9
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guoyangzhen Mar 20, 2026
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5 changes: 5 additions & 0 deletions .changeset/fix-sse-chunked-encoding.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@modelcontextprotocol/server': patch
---

Add Transfer-Encoding: chunked header to SSE responses in WebStandardStreamableHTTPServerTransport. Prevents HTTP/2 PROTOCOL_ERROR with adapters like @hono/node-server that buffer responses and add Content-Length headers.
3 changes: 3 additions & 0 deletions packages/server/src/server/streamableHttp.ts
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Expand Up @@ -450,6 +450,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
const headers: Record<string, string> = {
'Content-Type': 'text/event-stream',
'Cache-Control': 'no-cache, no-transform',
'Transfer-Encoding': 'chunked',
Connection: 'keep-alive'
};

Expand Down Expand Up @@ -503,6 +504,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
const headers: Record<string, string> = {
'Content-Type': 'text/event-stream',
'Cache-Control': 'no-cache, no-transform',
'Transfer-Encoding': 'chunked',
Connection: 'keep-alive'
};

Expand Down Expand Up @@ -751,6 +753,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
const headers: Record<string, string> = {
'Content-Type': 'text/event-stream',
'Cache-Control': 'no-cache',
'Transfer-Encoding': 'chunked',
Connection: 'keep-alive'
};

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