Claude Sonnet 5 — close to Opus, at Sonnet price

Anthropic shipped Sonnet 5 on June 30. It lands close to Opus 4.8 on agentic and knowledge-work evaluations at $2/$10 per million tokens through August. The one number to watch is the new tokenizer, which counts up to 1.35x more tokens, so measure real spend before you size a budget.

See Which work to move, and the token-bill catch

Sonnet 5 is now the default on Free and Pro. For builders the practical move is to put multi-turn agent loops and batch jobs on claude-sonnet-5, keep Opus 4.8 for the hardest one-shot reasoning, and try medium reasoning effort before escalating.

Two numbers worth holding onto: the introductory $2/$10 per-million rate runs only through August 31, then steps to $3/$15. And the updated tokenizer counts roughly 1.0 to 1.35x more tokens for the same text, so the rate card understates a long-context job. Run one real task, compare the actual token counts, and budget off the measured number.

The full decision walk-through →