[BUG] zlibError decompression failures on session start and command execution

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Image
Bug Description
i am using claude code with litellm and i keep getting decompression error: ZlibError but claude code works but it spams my ui with this error, i can avoid the issue by using alias claude ='claude 2> /dev/null' but i hope there can be a better fix for this. i am using the native build of claude code.. the old js version does not have this issue and if i use claude --debug it does not give my any indication of why the error is happening

Environment Info

Platform: darwin
Terminal: WarpTerminal
Version: 2.1.107

Feedback ID: ebf2a7c7-86d6-4c89-bce2-dc852fc25a94
https://github.com/anthropics/claude-code/issues/20199
https://github.com/anthropics/claude-code/issues/18302

What Should Happen?

no ZlibError spam in terminal/ghostty

Error Messages/Logs

osalloum
on Feb 7 · edited by osalloum
Author
I think that this bug is related to non streaming api calls which claude code does , when one of those fails, we get spammed with zlib error
Claude code does a lot of misc calls to generate custom titles , check token sizes, etc

I fixed the core issues in litellm but in the meanwhile if the specific issue you are facing is not impacting your core experience , you can just pipe error output to /dev/null


claude 2> /dev/null


ernestkoe
on Mar 7
Claude and I have a theory on what's happening:

HTTP MCP transport is sending compressed gzip that the client isn't handling.

The SDK uses fetch directly — it doesn't set Accept-Encoding, but Bun's fetch might auto-negotiate gzip. The issue is likely that the SSE event stream is being compressed by the server but the SDK's SSE parser can't handle it. The fix is to tell the server not to compress by adding Accept-Encoding: identity to the request headers:

Steps to Reproduce

just start claude in terminal (any terminal). Wait.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.105

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_