Opus 5 feels like a serious regression from Opus 4.8. Two concrete patterns from daily use: 1. **Destructive file editing.** Opus 5 destroyed large portions of my CLAUDE.md (my critical, hand-maintained memory/config file, ~550KB): it ran a find-replace script with a non-unique anchor and silently deleted a huge chunk of the text (over 60% lost). I only recovered it thanks to OneDrive version history. This never happened with any other model in months of daily use. 2. **Iterating on symptoms i

Opus 5 regression vs Opus 4.8: destructive file edits and symptom-chasing on UI refinements

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Activity 0 comments · opened Aug 2, 2026

Opus 5 feels like a serious regression from Opus 4.8. Two concrete patterns from daily use:

Destructive file editing. Opus 5 destroyed large portions of my CLAUDE.md (my critical, hand-maintained memory/config file, ~550KB): it ran a find-replace script with a non-unique anchor and silently deleted a huge chunk of the text (over 60% lost). I only recovered it thanks to OneDrive version history. This never happened with any other model in months of daily use.

Iterating on symptoms instead of diagnosing. On a small UI refinement (a status pill misaligning cards in a grid) it iterated three times, each time fixing the symptom it was pointed at instead of stopping to find the actual cause (space added only to some cards, breaking row alignment). Opus 4.8 handled these refinement loops noticeably better.

As a user I'm switching away from Opus 5 for this kind of work.

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Environment: Claude Code (VS Code extension) on Windows 11; model claude-opus-5.