The short answer
Claude Opus 5.5 vs Claude Sonnet 5.5: specs side by side
| Claude Opus 5.5 | Claude Sonnet 5.5 | |
|---|---|---|
| Made by | Anthropic | Anthropic |
| Released | September 22, 2026 | September 28, 2026 |
| API model ID | claude-opus-5.5 | claude-sonnet-5.5 |
| Context window | 1M tokens | 1M tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Knowledge cutoff | Not published | June 2026 |
| Inputs | Text, images and files | Text, images and files |
| API price | $4 input / $20 output per 1M tokens | $2 input / $10 output per 1M tokens |
| In AimiChat | Genius quality · Aimi Genius ($100/month) | Balanced quality · Aimi+ ($15/month) |
Which to use for each task
Everyday writing and coding
Sonnet 5.5 handles most tasks well at half the API cost.
High-stakes decisions and analysis
Opus 5.5 is Anthropic's strongest model and is more careful about the figures and sources it states.
Large codebase work
Opus 5.5 is built for long, multi-file changes and code review.
High-volume drafting
Sonnet 5.5's lower cost makes it the better default for many short tasks.
What to know before you choose
Claude Sonnet 5.5 shipped six days after Opus 5.5 and closes much of the gap on everyday work, so Opus 5.5 earns its higher price mainly on long, open-ended tasks that need sustained judgment.
In AimiChat, Claude Sonnet 5.5 is available from the Aimi+ plan and Claude Opus 5.5 on the Aimi Genius plan.
Published benchmarks
Each company reports different tests with different settings, so these are listed per model rather than head to head.
| Model | Benchmark | Score | Reported by |
|---|---|---|---|
| Claude Opus 5.5 | Terminal-Bench 4.0 (xhigh effort) | 66.4% | Anthropic launch post |
| Claude Opus 5.5 | GDPval-AA v2.1 (knowledge work) | 1846 | Anthropic launch post |
| Claude Opus 5.5 | Humanity's Last Exam (with tools) | 67.7% | Anthropic launch post |
| Claude Opus 5.5 | OSWorld 2.0 (partial credit) | 81.8% | Anthropic launch post |
| Claude Sonnet 5.5 | Terminal-Bench 4.0 | 70.6% | Anthropic launch post |
| Claude Sonnet 5.5 | GDPval-AA v2.1 (knowledge work) | 1844 | Anthropic launch post |
| Claude Sonnet 5.5 | Humanity's Last Exam (with tools) | 64.5% | Anthropic launch post |
Try both in AimiChat
Claude Opus 5.5 runs on the Genius quality and Claude Sonnet 5.5 on Balanced. On a plan that includes both, you can send the same prompt twice in one chat, switching quality in between, and compare the answers directly. Read more about Claude Opus 5.5 and Claude Sonnet 5.5, or see which plan includes which model.
Sources
Specifications and prices come from the model makers and API listings below. Benchmark figures are reported by the company that made the model and are not independent tests.