Anthropic ships Claude Sonnet 5.5, near Opus 5.5 at half the price
Anthropic released Claude Sonnet 5.5 on September 28, 2026 at Sonnet 5's price of $2 per million input tokens and $10 output. Anthropic says it runs more than 30% faster than Sonnet 5 and uses up to 30% fewer tokens per task. It reports 70.6% on Terminal-Bench 4.0, against 10.3% for Sonnet 5. It is the first Sonnet with the cyber safeguards used on Opus 5.5, and higher-risk security tasks fall back to Sonnet 5.
Why it matters
It scores 56 on the Intelligence Index, two points behind Opus 5.5 and ahead of Fable 5.1 and GPT-6 Astra, at half Opus 5.5's price. For most agent work the mid tier is now close enough to the top that the price gap decides.
Who should care
Anyone on Sonnet 5, and teams paying for Opus on tasks Sonnet may now handle
What you can do
Swap to claude-sonnet-5-5 and set the thinking mode to between_tools, since turning thinking off is no longer accepted. Then compare it with Opus 5.5 on your hardest tasks.