Anthropic has released Opus 5.5, a new flagship model that the company claims sets a state-of-the-art in coding and knowledge work performance. According to the announcement, Opus 5.5 outperforms the larger Fable model on many benchmarks and completes several informal tasks that Fable could not. The model is also cheaper: output tokens are priced at $20 per million, down from $25 for the previous Opus 5, with similar reductions across other pricing metrics. Opus 5.5 is faster to serve, reflecting a lower compute cost.

The new version also changes how the model communicates, with reduced jargon and a tendency to place important information at the start of its messages. The release comes just two months after Opus 5, which launched on July 24th. Anthropic notes that Sonnet 5.5 and Haiku 5.5 are expected in the coming weeks with similar performance improvements.

Opus 5.5 is described as comparable to Mythos in biology and cybersecurity capabilities, and its release is subject to the same safeguards used for Fable. These safeguards restrict the model’s use in discovering exploits in compiled programs and developing recognizable biological weapons, among other tasks. This is the first model release since CEO Dario Amodei embraced the idea of pacing the frontier, deliberately slowing capabilities advancement to allow alignment and safety work to catch up. In a post earlier this month, Amodei wrote that fully addressing risks requires even more prudence, not just investing in risk prevention but pacing capabilities growth.

Safety training for Opus 5.5 was broadly similar to previous models, with alignment testing and pre-release evaluation by external organizations such as METR and Frontier Design. Anthropic says it is preparing more advanced training and evaluation systems for future models, including improved security and monitoring. The company believes public policy should play a larger role in ensuring safety as AI becomes more capable, and it has begun building the infrastructure to support that; more details are expected soon.