Anthropic Launches Claude Sonnet 5.5 as Developers Test One-Prompt Game Builds

Anthropic released Claude Sonnet 5.5 on September 28, positioning the model as a faster, lower-cost companion to Claude Opus 5.5 while developers test it in ambitious one-prompt coding demos, including a Mario Kart-style kart racer. The launch makes Anthropic's newest Sonnet model available across its main consumer, developer and cloud channels, and it sharpens the company's pitch that routine agentic work should not always require its most expensive flagship model.