Anthropic released Claude Sonnet 5, calling it its most agentic Sonnet yet, capable of planning, tool use, and operating autonomously, and saying that at higher effort levels it approached Opus 4.8 at lower cost. It improved substantially over Sonnet 4.6 in reasoning, tool use, coding, and knowledge work, with gains on agentic search (BrowseComp) and computer use (OSWorld-Verified). Introductory pricing of $2 and $10 per million input and output tokens was made permanent, and the model was available on every plan from Free to Enterprise. On safety, Anthropic reported a lower overall rate of undesirable behaviors than Sonnet 4.6, cyber safeguards on by default, and substantially less capability for developing software exploits than the Opus models. An updated tokenizer meant token counts could rise by 1.0 to 1.35x for the same text. The release coincided with the announcement lifting export controls on Fable 5.