TL;DR: Claude Sonnet 5.5, released September 28, 2026, is a faster, cheaper model built for well-scoped everyday work – fixing bugs, iterating on features, and creating polished documents, slides and spreadsheets. It runs 30%+ faster than Sonnet 5, costs up to 30% less per task, and holds pricing at $2/$10 per million tokens with a 1 million token context window.
Claude Sonnet 5.5 is the second model in the Claude 5.5 family, arriving six days after Opus 5.5. For many developers it may become the daily driver because it hits most of Opus-level quality at a fraction of the cost.
What Sonnet 5.5 Is Best At
- Fixing bugs – fast, well-scoped debugging
- Iterating on features – quick edit-and-run loops
- Polished documents – clear writing, human-like tone
- Slides and spreadsheets – with a strong eye for design
The Numbers That Matter
| Metric | Value |
|---|---|
| Speed | 30%+ faster output than Sonnet 5 |
| Cost | Up to 30% less per task |
| Price | $2 input / $10 output per M tokens |
| Context | 1M tokens, up to 128K output |
| Terminal-Bench 4.0 | 70.6% (agentic coding) |
Why the Cheaper Model Is a Big Deal
Sonnet 5.5 nearly matches Opus 5.5 on several benchmarks while costing up to 30% less per task. On the agentic coding test, the cheaper model even edges ahead. For everyday development, that combination of speed and price is hard to beat.
A Note on Watermarking
Sonnet 5.5 writes more clearly and in a more human-like way, and it also includes invisible text watermarking – worth knowing if you publish AI-assisted content.
How to Use It Well
Give Sonnet 5.5 well-scoped tasks with clear acceptance criteria. Save open-ended, high-judgment problems for Opus 5.5. This split keeps your speed high and your bill low.
Put It to the Test
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