Claude Sonnet 4.5 is an AI model released by Anthropic on Sep 29 2025, 55 days after Claude Opus 4.1. It is the 14th tracked release from Anthropic out of 19 total.
On published benchmarks, it scores 83.4% on GPQA Diamond (graduate-level science reasoning), 77.2% on SWE-Bench Verified (real-world software engineering), 68% on MMMU (multimodal understanding).
About Anthropic: AI safety company building the Claude family of models. Founded in 2021 by former OpenAI researchers.