Claude Opus 5.5 vs Claude Sonnet 5.5
Claude Opus 5.5 (Anthropic) and Claude Sonnet 5.5 (Anthropic) compared point by point: measured performance, pricing, context and capabilities.
Data as of October 22, 2026
Side-by-side comparison
| Criterion | Claude Opus 5.5 | Claude Sonnet 5.5 |
|---|---|---|
| Developer | Anthropic | Anthropic |
| Released | September 22, 2026 | September 28, 2026 |
| Capability index | 95.9 / 100 | 95.9 / 100 |
| Input price | $4 | $2 |
| Output price | $20 | $10 |
| Cost of a typical task | $0.12 | $0.06 |
| Context window | 1,000,000 tokens | 1,000,000 tokens |
| Maximum output | 128,000 tokens | 128,000 tokens |
| Reasoning mode | Yes | Yes |
| Tool calling | Yes | Yes |
| Accepted inputs | text, image, PDF | text, image, PDF |
| Open weights | No | No |
| Knowledge cutoff | June 2026 | June 2026 |
Two models head to head
Claude Opus 5.5 and Claude Sonnet 5.5 are two frontier models, the ones you pick when quality comes first, both built by Anthropic. Claude Opus 5.5 was released on September 22, 2026, Claude Sonnet 5.5 on September 28, 2026.
All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.
Which one is more capable?
On our capability index, Claude Opus 5.5 scores 95.9 out of 100 and Claude Sonnet 5.5 95.9. The gap is too small to separate them.
On the 5 benchmarks reported for both, Claude Opus 5.5 wins 2 times and Claude Sonnet 5.5 2:
- GPQA Diamond (PhD-level science questions): Claude Opus 5.5 90.6%, Claude Sonnet 5.5 95.6%
- OTIS Mock AIME (competition mathematics problems): Claude Opus 5.5 100%, Claude Sonnet 5.5 100%
- FrontierMath (very hard research-level mathematics): Claude Opus 5.5 91.2%, Claude Sonnet 5.5 88.8%
- FrontierCode (advanced programming tasks): Claude Opus 5.5 54.6%, Claude Sonnet 5.5 52.1%
- APEX-Agents (professional tasks carried out by an agent): Claude Opus 5.5 73.5%, Claude Sonnet 5.5 75.5%
Budget
Claude Opus 5.5 costs $4 per million input tokens and $20 per million output tokens; Claude Sonnet 5.5 costs $2 and $10.
For a typical agent task (read 20,000 tokens, write 2,000), expect $0.12 with Claude Opus 5.5 versus $0.06 with Claude Sonnet 5.5. Claude Sonnet 5.5 is 2 times cheaper, a gap that adds up quickly over 1,000 tasks: $60 difference.
Run the numbers with your own volumes in the agent cost calculator.
Context and capabilities
Both models have the same context window: 1,000,000 tokens, roughly 1,500 pages.
Reasoning mode: Claude Opus 5.5 yes, Claude Sonnet 5.5 yes. Tool calling: Claude Opus 5.5 yes, Claude Sonnet 5.5 yes. Image input: Claude Opus 5.5 yes, Claude Sonnet 5.5 yes.
Neither publishes its weights: both are used through an API.
Knowledge cutoff: June 2026 for Claude Opus 5.5, June 2026 for Claude Sonnet 5.5.
In short
Our reading of the data:
- Choose Claude Sonnet 5.5 for a lower cost.
This verdict relies on public figures; it does not replace a trial on your own tasks.
Other comparisons
Frequently asked questions
Claude Opus 5.5 or Claude Sonnet 5.5: which is better?
On our index (Epoch AI data), Claude Opus 5.5 scores 95.9 and Claude Sonnet 5.5 95.9 out of 100. The best choice also depends on price and on your use case.
Which one is cheaper?
Claude Sonnet 5.5. To read 20,000 tokens and write 2,000, expect $0.12 with Claude Opus 5.5 and $0.06 with Claude Sonnet 5.5 (prices as of October 22, 2026).
Which one has the larger context window?
Neither: both accept 1,000,000 tokens.
Can I run Claude Opus 5.5 or Claude Sonnet 5.5 on my own servers?
No: both are closed models, available through an API.
Data sources
- Models.dev — Model data: models.dev (open-source project)
- OpenRouter — Market prices cross-checked with OpenRouter
- Epoch AI — AI Benchmarking Hub — Epoch AI, “AI Benchmarking Hub”, epoch.ai, CC BY 4.0
Data as of October 22, 2026
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