What is new in Claude 5.5?

Anthropic unveiled Claude Opus 5.5, which performs at the level of Claude Fable-5.1 on most tasks and costs 40% less to run than Opus 5. The model communicates more naturally and writes more clearly, while being 85% less likely to attempt to bypass its prescribed boundaries. It also fixed a codebase in three hours which Opus-5 took over 20 hours.