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Claude Code Cuts CPU Usage and Speeds Up Startup, Resume, and Fullscreen Mode

Claude CodeView original changelog

Claude Code 2.1.268 fixed a busy loop that pinned a CPU core during long-running idle sessions and during rapid terminal focus reports in a session recap, addressing a sustained high-CPU-usage complaint. The same release made fullscreen mode repaint prompt-line changes as fast as typing a character, sped up --continue and --resume so the conversation appears immediately instead of waiting on SessionStart hooks and a full transcript re-read, reduced unnecessary redraws during tool-heavy turns, and cut startup time in projects that use .claude/workflows/ scripts by no longer parsing each script just to list them.

Key Takeaways

  • A busy loop was pinning a CPU core in idle, long-running sessions, a bug that could go unnoticed until fan noise or battery drain gave it away; it is fixed in this release.
  • Rapid terminal focus reports during a session recap were also driving up CPU usage, a second trigger for the same underlying loop.
  • --continue and --resume now show the conversation immediately instead of blocking on SessionStart hooks, and the first message no longer re-reads the whole transcript.
  • Fullscreen mode's Shift+Enter prompt editing is now as fast as typing a character, replacing a re-render of the visible transcript with a targeted repaint.
  • Tool-heavy turns redraw less, since a hidden per-tool-batch reminder no longer forces a transcript refresh it does not need.
  • Projects using .claude/workflows/ scripts start faster, because listing those scripts no longer requires parsing each one first.

Fixing a Sustained High-CPU Bug

Claude Code 2.1.268 fixed a busy loop that could pin a CPU core in two specific situations: long-running idle sessions, and rapid terminal focus reports arriving during a session recap. Neither should have consumed meaningful CPU while idle, and both now behave accordingly. This was one of the more disruptive performance bugs still open, since a pinned core in an idle terminal session is easy to miss until a machine's fan spins up or its battery drains unexpectedly.

Faster Startup, Resume, and Fullscreen Interaction

Several related changes shaved latency off common everyday actions. Resuming a session with --continue or --resume now shows the conversation immediately instead of waiting for SessionStart hooks to finish, and the first message no longer re-reads the entire transcript. Fullscreen mode now repaints as fast as typing a single character when a prompt line is added or removed with Shift+Enter, rather than re-rendering the visible transcript on every keystroke of that kind. Claude Code also cut unnecessary redraw work during tool-heavy turns by no longer refreshing the transcript for a hidden per-tool-batch reminder that does not need to be shown.

Separately, projects that use .claude/workflows/ scripts start faster: Claude Code previously parsed every script in that folder just to list them at startup, and now avoids that work entirely. Together with the CPU fix, this release targets the everyday responsiveness of the terminal UI rather than any single new feature.