Claude Sonnet 5

Anthropic's "most agentic Sonnet model yet" (API: `claude-sonnet-5`): plans, uses tools like browsers and terminals, and runs autonomously, approaching Opus-class quality at mid-tier cost. 1M-token context with adaptive reasoning; ships with a new tokenizer that yields roughly 1.0–1.35x more tokens for the same input than prior Claude models. Introductory pricing $2/$10 per million input/output tokens through August 31, 2026, then $3/$15. Default model for Free and Pro plans. AA Intelligence Index 53 (v4.1, adaptive reasoning at max effort) — #5 overall at release.