Anthropic has upgraded Claude Sonnet, replacing Sonnet 4.6 from February with Sonnet 5 as the best medium-sized model, described as the "most agentic Sonnet model yet." The company states Sonnet 5 "can make plans, use tools like browsers and terminals, and run autonomously at a level that, just a few months ago, required larger and more expensive models," and that its "performance is close to that of Opus 4.8, but at lower prices." Sonnet 5 is the new default model for Claude free and pro users, available at an introductory price of $2 per million input tokens and $10 per million output tokens through August 31, 2026, after which standard pricing becomes $3 per million input tokens and $15 per million output tokens. Anthropic also has its most capable Mythos 5 and Fable 5 models, with Mythos 5 having fewer guardrails for select security researchers and platform owners, and Fable 5 being a safer version briefly available before being blocked by the U.S. government. Claude Opus 4.8 arrived at the end of May, and Claude Sonnet 5 arrives four months after the previous Sonnet 4.6 release. Earlier today, Anthropic also released a new desktop app with Claude Science for Mac and Linux.