[BUG] Text response became much slower in a version between 2.1.50 and 2.1.75

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?

On the latest version (~2.1.75), the text response in the Claude Code became much slower.

• If I ask my Claude Code a question or to do a task, when it is giving its conclusion / summary, it prints texts line by line, with tens of millisecond delay after each line.
• This problem started around March 5-6, 2026.
• In comparison, when Claude Code is making code changes, it prints the colored diff on the screen in one chunk, much faster. This discrepancy is consistent.

I'm using Claude Code on an enterprise Max-tier plan, in Ubuntu Linux 24.04, in terminal emulators such as 'foot' and 'ghostty'. My computer is connected to the Internet via Ethernet and then Fiber in the Palo Alto, CA. The ping latency to most major websites are very low.

An earlier version (2.1.50) of Claude Code doesn't suffer from this problem. On this version and earlier versions, Claude Code prints its conclusion / summary in one chunk, rather than line by line with delay between them.

I'm sure that something happened between 2.1.50 and 2.1.75, but I don't know which exact version introduced this problem.

One absurd thing is that some of my coworkers suffer from this same problem, but some don't (even on the latest version and same OS, same terminal emulator).

What Should Happen?

Claude Code should print its conclusion / summary to user requests in one chunk, at least not line by line.

Error Messages/Logs

No error messages associated with them.

Steps to Reproduce

Steps:

1. Have a fresh installation of Claude Code at 2.1.75.
2. Enter Claude Code from command line in a Linux terminal emulator (e.g., foot, ghostty)
3. Ask a simple question (e.g., "Help me review my CLAUDE.md")
4. When it is giving its conclusion to you, it prints line by line, with at least tens of milliseconds delay after each line.
5. In comparison, when Claude Code is making code changes, it prints the colored diff on the screen in one chunk, much faster consistently.

Both Opus 4.6 and Sonnet models suffer from this problem.

Comparison:

• I also have a machine at an old version 2.1.50. That version doesn't suffer from this problem. But then it got auto-updated to 2.1.75, it immediately started having this slowness problem.
• On any machine, if I uninstall the native-binary Claude Code at 2.1.75, and install Claude Code v2.1.50 via npm (because this seems the only way to install an older version), then the problem is gone.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.50 (didn't have time to bisect, but I've verified that this version works)

Claude Code Version

2.1.75

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

• Configuration file is empty (just {})
• A very small codebase is sufficient to reproduce this problem