Anthropic launched Claude 3.7 Sonnet, its first hybrid reasoning model, with a standard mode for quick answers and an extended thinking mode that shows its step-by-step reasoning on hard problems. Users could control how long the model thought.

The launch arrived alongside Claude Code, Anthropic's agentic command-line coding tool, signaling a shift toward models that do extended work rather than just answer questions. Extended thinking quickly became the template for reasoning modes across the industry.

Claude 3.7 Sonnet bridged the Claude 3 and Claude 4 generations, keeping Anthropic competitive in coding while the next flagship was still in training.