What is Claude Opus 5.5?

Large language models are computer programs trained on a vast amount of text so they can generate, summarize, translate and analyze language. Their output can be less reliable when the training data is biased or inaccurate, and extra software can give them memory and tools such as web search so they can do more than chat. Claude Opus 5.5 is a model from Anthropic, introduced on September 22, 2026 as the first model in its Claude 5.5 family. Anthropic's documentation describes it as intended for long-running agentic coding and knowledge work, meaning extended tasks in which the model carries out many steps, such as writing software.

Written from primary sources and reference pages, and checked against them by an independent AI fact-checker. Drafted with AI assistance.