[BUG] High sustained CPU usage (~100% per instance) even when idle

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?

Description

Two instances of Claude Code CLI running simultaneously each consume ~100% CPU sustained, even between interactions when both should be idle. On a 4-core machine this makes the system noticeably sluggish.

Environment

• Claude Code version: 2.1.29
• Node.js: v22.19.0
• OS: Linux Mint 21.3 (kernel 5.15.0-164-generic)
• Hardware: 4 CPU cores, 7.5 GB RAM
• Terminal: Guake (but issue is in the claude process itself)

Observed behavior

Both claude processes pin at ~100% CPU each continuously, even when no tool calls are running and no output is being streamed:

PID USER %CPU %MEM RES COMMAND
3225 jan 102% 9.6% 756 MB claude
5342 jan 89% 8.4% 660 MB claude

A second measurement 2 minutes later with both sessions idle between interactions:

PID USER %CPU %MEM RES COMMAND
3225 jan 101% 9.9% 781 MB claude
5342 jan 97% 9.0% 705 MB claude

Each process has ~13-14 threads. Virtual memory mapped is ~71 GB per process (normal for V8 but noted for completeness).

---

What Should Happen?

Expected behavior

Between interactions, CPU usage should drop to near zero since the CLI is mostly waiting for user input or network responses.

Error Messages/Logs

Steps to Reproduce

1. Open two terminal tabs
2. Run claude in each
3. Have a conversation in one; leave the other idle
4. Observe CPU usage with top

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.29

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

• No MCP servers configured
• The high CPU is in the claude Node.js process itself, not in any child/tool processes
• Single instance also shows ~100% CPU, it's not contention between the two