Summary
Claude Sonnet 5.5 runs more than 30% faster and costs up to 30% less than Sonnet 5. Anthropic reports a jump from 10.3% to 70.6% on Terminal-Bench 4.0, alongside gains in long-horizon work and image understanding.
Why it matters
The release pushes frontier-level coding and knowledge work into a lower-cost model tier, increasing the economic viability of persistent agents.
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