September 24, 2026
Opus 5.5 hunts down terminal startup slowdowns: .zshrc fixes
On September 24, 2026, Opus 5.5 found many optimizations for launching a new shell session that other models missed. This involves .zshrc and related files.
Guillermo Rauch
@rauchg
ShellPerfBench. I am painfully particular about how long it takes to start a new shell session. Opus 5.5 found many great optimizations that other models missed. Folks, every time you open a new terminal, you may be suffering quietly. Ask your agent to optimize .zshrc and related files.
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Now Opus 5.5 found them in ShellPerfBench. Terminal startup lag can easily go unnoticed until a new session is launched again and again.
In this story, Opus 5.5 checked not application code, but the startup of a working terminal.
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