Opus 4.8 vs. Opus 5: Tied scores but divergent engineering behaviors
bisonbear2 · reddit · 2026-08-26
The author compared Opus 4.8 and Opus 5 on 25 real tasks from their own repository. Both models passed 9 tasks strictly, but exhibited different behaviors:
- Opus 5: Searched wider and verified more. Used more shell commands (18/25), more test commands (15/25), and touched more files, spending budget on discovery and validation.
- Opus 4.8: Stayed contained. Had a smaller patch footprint (20/25), staying closer to the merged change, spending budget on editing.
Cost-wise, Opus 5 was 1.4% cheaper on typical tasks due to task patterns, despite using 4% more tokens and time. The post argues that pass rates hide differences in search strategy, verification depth, and maintainability.
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