Anthropic Launches Claude Opus 5.5: Fable 5.1-Level Performance at 40% Lower Cost
aigclink · x · 2026-09-23
Anthropic introduced Claude Opus 5.5, the first model in its new Claude 5.5 family and its new flagship.
Key points:
- Performance: Matches Claude Fable 5.1 on most work while running 40% cheaper than Opus 5. One tester completed a 680,000-line code migration in under a day — work that would take an engineering team weeks. It succeeded 39/40 times at cutting web app load times without altering behavior, and beat other Claude models on a single-prompt game build for graphics and polish.
- Safety: Best scores to date on Anthropic's automated behavioral audit; less likely to take hard-to-reverse actions or act outside boundaries, and more resistant to prompt injection than Opus 5. Tested pre-release by external evaluators including Frontier Design and METR, with alignment testing expanded to longer tasks, impossible tasks, and scenarios modeled on real incidents.
Related event: Anthropic Launches Claude Opus 5.5: 40% Cheaper, 30% Faster(68 posts)→
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