claude-code - 💡(How to fix) Fix [BUG] claude-code 2.1.110 no longer sending DEC 2026 messages on terminals that support it [3 comments, 2 participants]

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anthropics/claude-code#49584Fetched 2026-04-17 08:37:01
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  • I have searched existing issues and this hasn't been reported yet
  • This is a single bug report (please file separate reports for different bugs)
  • I am using the latest version of Claude Code

What's Wrong?

Claude Code has supported the DEC 2026 synchronized output terminal extension for some time, which can help to reduce screen tearing and other artifacts when Claude redraws the scrollback buffer.

Since Claude 2.1.110, I've noticed Claude is no longer sending DEC 2026 enable/disable commands on my terminal which supports it. I use a modified version of the Emacs eat terminal emulator, which uses a TERM value of eat-truecolor. Its terminfo advertises the Sync capability, and it responds to DECRPM queries to test for the availability of the feature. I also tested setting my TERM value to xterm-256color to match iTerm, and Claude also does not send the sync messages.

Meanwhile, if I set my TERM to xterm-ghostty or xterm-kitty, Claude continues to send DEC 2026 instructions.

What Should Happen?

I assume Claude is now relying on a hardcoded list of terminal which support this feature, but this penalizes us users who run more obscure terminal emulators. Claude should support checking for DEC 2026 support using the DECRPM instruction, or a hardcoded list plus looking for the Sync feature in the terminfo (ghostty includes this feature in its custom terminfo, but other emulators such as iTerm that rely on a standard terminfo such as xterm-256color do not).

Error Messages/Logs

Steps to Reproduce

Launch claude in an affected terminal. When Claude produces a large amount of output, screen tearing will occur.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.109

Claude Code Version

2.1.112

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

No response

extent analysis

TL;DR

The issue can be fixed by modifying Claude Code to check for DEC 2026 support using the DECRPM instruction or by adding a check for the Sync feature in the terminfo.

Guidance

  • Investigate the change in Claude Code between versions 2.1.109 and 2.1.110 to identify the introduction of the hardcoded list of terminals that support DEC 2026.
  • Modify the code to include a check for the Sync feature in the terminfo, in addition to the hardcoded list, to support more terminal emulators.
  • Test the modified code with different terminal emulators, including the modified Emacs eat terminal emulator, to ensure that DEC 2026 enable/disable commands are sent correctly.
  • Consider adding a configuration option to allow users to specify whether to use the DECRPM instruction or the hardcoded list to determine DEC 2026 support.

Example

No code snippet is provided as the issue does not include specific code details.

Notes

The fix may require changes to the Claude Code source code, and the exact implementation will depend on the code structure and requirements. Additionally, the issue may be specific to certain terminal emulators or environments.

Recommendation

Apply a workaround by modifying the Claude Code to check for DEC 2026 support using the DECRPM instruction or by adding a check for the Sync feature in the terminfo, as this will provide a more flexible and compatible solution.

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