Anthropic launched Claude Sonnet 5 on 2026-06-30 as its most agentic Sonnet yet, available across all plans (default for Free and Pro) and via the API as claude-sonnet-5, with four new effort levels (low / medium / high / xhigh), introductory pricing of $2 per million input tokens and $10 per million output tokens through August 31, 2026 — rising to $3 / $15 standard on September 1, 2026 — and a published system card showing Sonnet 5 in some cases matching Opus 4.8 on agentic search (BrowseComp) and computer use (OSWorld-Verified). The same Sonnet 5 launch also ships with a 1.0–1.35x tokenizer change, cyber safeguards enabled by default, a Sonnet 4.6 → Sonnet 5 misaligned-behavior improvement (still higher than Opus 4.8 and Claude Mythos Preview), and a 0.0% full-working-exploit score on the Firefox 147 evaluation Anthropic developed with Mozilla.
Claude Sonnet 5 narrows the gap to Opus 4.8 at $2/$10 → $3/$15 per MTok