Anthropic ships Claude Opus 5.5: 40% cheaper than Opus 5, does a 680k-line code migration in a day
evilrabbit_ · x · 2026-09-23
Anthropic introduced Claude Opus 5.5, the first model in its Claude 5.5 family, matching Fable 5.1-level performance at 40% lower cost than Opus 5, with pre-release testing by Frontier Design and METR.
- Performance: early testers completed a 680,000-line code migration in under a day; it cut load times across a web app in 39 of 40 attempts without breaking behavior; it topped a single-prompt game-building test on graphics and polish.
- Safety: best scores yet on Anthropic's automated behavioral audit across thousands of simulated scenarios, less likely to take hard-to-reverse actions, more resistant to prompt injection, with alignment testing extended to longer and impossible tasks.
- rauchg praised the release's taste, arguing AI removes any excuse not to push web design forward.
Related event: Anthropic Launches Claude Opus 5.5: Smarter, Faster and 40% Cheaper(54 posts)→
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