Anthropic dropped Claude Sonnet 5 on June 30, and the positioning is deliberate: this is the most agentic Sonnet model they've shipped. Close to Opus 4.8 in performance, at 40% lower cost at standard pricing, and 60% cheaper during the introductory window that runs through August 31, 2026. For anyone running multi-step agents at scale, this changes the cost math in a concrete way. What's actually in the release Sonnet 5 ( claude-sonnet-5 ) sits between Haiku 4.5 and Opus 4.8 in the lineup, but Anthropic is pitching it as the default workhorse for most agentic work. It carries a 1M token context window, 128k max output, and adaptive thinking. Fast latency. And it defaults to effort: high on the Claude API and Claude Code, meaning the model engages its full reasoning budget by default. That's the same default as Opus 4.8. Here's the full pricing picture now: Haiku 4.5 : $1/$5 per million tokens. Fast, near-frontier for simple tasks. Sonnet 5 intro (through Aug 31)...