Claude 1 is Anthropic’s first publicly released language model, launched in March 2023 alongside the smaller, faster Claude Instant. It came out a few months after Anthropic first previewed Claude to a small group of partner companies in late 2022, and it made Anthropic’s Constitutional AI training approach, using AI-generated feedback guided by a written set of principles instead of relying only on human raters, available through a commercial API for the first time. Claude 1 launched with a 9,000-token context window, small by later standards, though Anthropic expanded it to 100,000 tokens just two months after release, well ahead of most competing chat models at the time.
Anthropic has since retired Claude 1 in favor of the Claude 2 and Claude 3 model families, and the original API access for it is no longer offered. It matters mainly as the starting point of Anthropic’s model lineup and the first public proof that Constitutional AI training could produce a competitive assistant, setting expectations that later Claude generations would build on with much larger context windows, stronger reasoning, and multimodal input.