Claude Sonnet 5.5 is an announced but not yet released Anthropic model from the 5.5 generation. Word of it comes from the Claude Opus 5.5 announcement of 22 September 2026, in which Anthropic stated plainly that Claude Sonnet 5.5 and Claude Haiku 5.5 would follow "in the coming weeks".
Beyond the fact of the announcement there is no publicly confirmed data: Anthropic has not given an API model identifier, pricing, context window size, knowledge cutoff or any benchmark results. Nor has any release date more precise than "the coming weeks" been announced.
Context comes from the position of its siblings. The released Claude Opus 5.5 costs $4 per million input tokens and $20 per million output tokens, scoring 66.4% on Terminal-Bench 4.0, 81.8% on OSWorld 2.0, 1846 Elo on GDPval-AA v2.1 and 40.0% on AutomationBench — at 40% lower running cost than Opus 5. Under Anthropic's naming convention to date, the Sonnet variant sits below Opus in price and capability, but for the 5.5 generation this has not yet been confirmed by any official material. This entry will be completed after the model ships.
