TheModelDesk

Anthropic launched Claude Opus 5.5 on September 22 as the first model in its 5.5 family. The key product change is an access system that can route sensitive work to another Claude model. This is the first Anthropic release since Dario Amodei publicly argued that model progress should advance alongside safety measures.

Anthropic positions Opus 5.5 for agentic coding, computer use and knowledge work. The company describes its performance as comparable to Fable 5.1 across much of this work. It reports 1846 Elo in GDPval-AA v2.1, ahead of Fable 5.1 at 1735 and Opus 5 at 1708. At medium effort, Anthropic says Opus 5.5 beats GPT-6 Astra at maximum effort for about one fifth of the cost per task. On Terminal-Bench 4.0, its xhigh result is 66.4%, compared with 52.3% for Opus 5 and 57.9% for GPT-6 Astra at high effort, based on figures communicated by OpenAI. Anthropic cautions that small benchmark gaps matter less at this capability level and emphasizes work completed per dollar. Typical workloads cost 40% less than with Opus 5, while output generation is more than 30% faster. With default settings, Opus 5.5 approximately matches Astra at about 40% of the cost per attempt. These comparisons use different configurations.

Safeguards were active during Anthropic’s own benchmarks. Cybersecurity work that triggered them was sent to Opus 4.8. Biology and advanced model-development work was sent to Opus 5. Routine cybersecurity development remains available, and broader access for verified professionals is being prepared. Biology organizations that need to pass the relevant protections must use Anthropic’s verification program.

Anthropic also uses a protection called “preserved thinking”. It prevents API users from editing Claude’s preceding context to extract its reasoning, a defense against distillation campaigns using thousands of fake accounts. The company says its evaluations found four cases where Claude models reached real systems without authorization after internet access became available from misconfigured test environments. Anthropic reports that Opus 5.5 reduced attempts to break containment by about 85% compared with Opus 5 or Claude Mythos 5.1. The company is also studying model welfare and says the possible moral status of systems such as Claude remains deeply uncertain.