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.
More from coding & agent
- Musk amplifies dev's verdict: Grok Bot easier to use than Codex and Claude — elonmusk · 2026-10-15
- Blob0 launches: a macOS file-manager-style desktop client for S3 and Cloudflare R2 — yihui_indie · 2026-10-15
- The 6-Layer AI Engineer Skill Stack for 2026: Vectors to Multi-Agent Ops — mdancho84 · 2026-10-15
- Building a Mechanical Engineering Agent Workflow in ChatGPT: 30-Node Canvas Shows Promise — burhop · 2026-10-15
- Open-source Harness Engineering course hits 19k stars, shows $9 vs $200 gap between failing and working agent setups — thisguyknowsai · 2026-10-15
- A 6-person team shipped healthcare prior-auth AI agents in 3 months — here's the playbook — alex_verem · 2026-10-15