Claude Opus 5 aims to match or exceed Fable 5's performance on many tasks while being faster and half the price.
Opus 5 shows substantial gains over Opus 4.8 in agentic coding, computer use, and long-horizon knowledge work, setting new state-of-the-art benchmarks.
Opus 5 lacks full 'Juice' for cyber offense and bio threats due to deliberate avoidance of cyber training and smaller model size.
Safety classifiers trigger 85% less often than Fable's, permitting source code vulnerability analysis but blocking binary vulnerability discovery.
Opus 5 shows improved prompt injection resistance, reducing attack success rate from 7.14% to 0.54% in computer use environments.
Alignment scores are up, with reduced circumvention and reckless tool use, but concerns include overconfidence and overdramatic phrasing.
Automated alignment tests show high scores, but the report warns against conflating benchmark scores with true alignment, urging caution in messaging.