Sonnet 5.5 vs Opus 5.5 looks like a simple choice between cheap and smart, but the published numbers say otherwise. Anthropic charges $2 per million input tokens for Sonnet 5.5 and $4 for Opus 5.5, yet on Artificial Analysis data, Opus 5.5 at low effort scored one point higher than Sonnet 5.5 at medium effort (42 against 41) and cost four cents less per task ($0.55 against $0.59).
Opus 5.5 launched on September 22, 2026, and Sonnet 5.5 followed on September 28. This guide compares them on price, cost per task, benchmarks and everyday use, so you can choose without reading a developer changelog. It is an analysis of published data, not a hands-on test.
Key Takeaways
- Price: Sonnet 5.5 costs $2 and $10 per million input and output tokens. Opus 5.5 costs $4 and $20, exactly double.
- Cost per task: Sonnet 5.5 is cheaper at the same effort level, but at max effort it cost $7.60 per task against $5.98 for Opus 5.5.
- Quality: Sonnet 5.5 lands within roughly three points of Opus 5.5 on most of Anthropic’s benchmarks and beats it on Terminal-Bench 4.0.
- Where Opus wins: Anthropic says Opus 5.5 stays clearly stronger on complex, open-ended work that needs sustained judgment.
- Beginner rule: Use Sonnet 5.5 for everyday writing, slides and spreadsheets. Use Opus 5.5 for sourced research and high-stakes analysis.
Contents
- What is the difference between Sonnet 5.5 and Opus 5.5?
- How much do Sonnet 5.5 and Opus 5.5 cost?
- Is Sonnet 5.5 really cheaper than Opus 5.5 per task?
- How do Sonnet 5.5 and Opus 5.5 compare on benchmarks?
- Which model should you use for writing, slides and research?
- Are there safety or availability differences?
- Frequently Asked Questions
What is the difference between Sonnet 5.5 and Opus 5.5?
Opus 5.5 is built for complex work that needs careful judgment. Sonnet 5.5 is the faster, cheaper choice for well-scoped everyday tasks.
That is Anthropic’s own framing. In its Sonnet 5.5 announcement, the company calls Sonnet 5.5 the second model in the Claude 5.5 family and describes it as strongest at fixing bugs and producing polished documents, slides and spreadsheets. Its Opus 5.5 announcement says Opus 5.5, the first model in the family, performs at the level of Claude Fable 5.1 on most work while costing 40% less to run than Opus 5. A smaller model, Claude Haiku 5.5, is due in the coming weeks.
| Sonnet 5.5 | Opus 5.5 | |
|---|---|---|
| Release date | September 28, 2026 | September 22, 2026 |
| Anthropic’s positioning | Faster, lower-cost, everyday work | Complex work needing careful judgment |
| Price per 1M tokens (input / output) | $2 / $10 | $4 / $20 |
| Output speed at max effort | 138 tokens per second | 93 tokens per second |
| Context window | 1M tokens | 1M tokens |
| Thinking | Up-front thinking can be switched off | Thinking cannot be switched off |
| API name | claude-sonnet-5-5 | claude-opus-5-5 |
Sources: Anthropic launch pages for prices, dates and thinking; Artificial Analysis for speed and context window.
How much do Sonnet 5.5 and Opus 5.5 cost?
Sonnet 5.5 costs $2 per million input tokens and $10 per million output. Opus 5.5 costs $4 and $20, exactly double.
A token is a small chunk of text. You pay for the text you send in (input) and the text the model writes back (output). Both models charge $0.20 per million tokens for cache reads, which are repeated inputs the model has already seen, but cache writes differ: $2.50 for Sonnet 5.5 and $5 for Opus 5.5.
Here is a worked example at list prices. Sending 200,000 input tokens and getting 10,000 tokens back costs $0.50 on Sonnet 5.5 and $1.00 on Opus 5.5, before caching, as MyClaw’s comparison calculates and the arithmetic confirms.
Both prices moved recently. Sonnet 5.5 costs the same per token as Sonnet 5, but Anthropic says it needs far fewer tokens, so it runs up to 30% cheaper per task. Opus 5.5 is 20% cheaper per token than Opus 5 ($5 and $25 before), and Anthropic says typical workloads cost 40% less. Alongside the launch, Anthropic also raised five-hour usage limits on Pro, Max, Team and seat-based Enterprise plans.
Is Sonnet 5.5 really cheaper than Opus 5.5 per task?
Only at the same effort setting. Across settings, Opus 5.5 at lower effort often matches or beats Sonnet 5.5 for similar money.
“Effort” is a setting that controls how long a model thinks before answering. More effort means more tokens, which means a higher bill. Artificial Analysis scores both models at every effort level on its Intelligence Index, a blend of 10 evaluations, and also records the average cost per task. I put its numbers side by side:
| Effort | Sonnet 5.5 score | Sonnet 5.5 cost per task | Opus 5.5 score | Opus 5.5 cost per task | Cheaper at same effort |
|---|---|---|---|---|---|
| Low | 36 | $0.41 | 42 | $0.55 | Sonnet, 26% less |
| Medium | 41 | $0.59 | 51 | $1.34 | Sonnet, 56% less |
| High | 47 | $1.08 | 54 | $1.82 | Sonnet, 41% less |
| Xhigh | 52 | $2.74 | 56 | $3.46 | Sonnet, 21% less |
| Max | 56 | $7.60 | 58 | $5.98 | Opus, Sonnet costs 27% more |
Three matchups stand out. Opus 5.5 at low effort (42 points, $0.55) beats Sonnet 5.5 at medium (41 points, $0.59). Opus 5.5 at high (54 points, $1.82) beats Sonnet 5.5 at xhigh (52 points, $2.74). Opus 5.5 at xhigh (56 points, $3.46) ties Sonnet 5.5 at max (56 points, $7.60) for less than half the cost.
The reason is token use. At max effort, Sonnet 5.5 wrote about 193,000 output tokens per task, against 119,000 for Opus 5.5. Anthropic makes a similar point, noting that Sonnet 5.5 pairs best with Opus at lower effort, while at higher settings it can roughly match Opus at a similar cost.
Two caveats. This is one blended index, so your own tasks may differ. And Anthropic notes that two of the index’s tests were run on a pre-release Sonnet deployment with a since-fixed bug, which it expects understated Sonnet’s scores slightly, if at all. Also note that defaults differ: Sonnet 5.5 defaults to medium effort in the Claude apps and high on the Claude Platform, so comparing “default against default” is uneven.
How do Sonnet 5.5 and Opus 5.5 compare on benchmarks?
On Anthropic’s published benchmarks, Sonnet 5.5 lands within a few points of Opus 5.5 on most tests and beats it on one.
| Benchmark | What it measures | Sonnet 5.5 | Opus 5.5 |
|---|---|---|---|
| GDPval-AA v2.1 | Real work across 44 occupations | 1844 | 1846 |
| AA-Briefcase v1.1 | Long knowledge-work projects | 1811 | 1822 |
| OSWorld 2.1 (partial) | Using a computer | 80.1% | 81.8% |
| CursorBench 4.0 | Coding tasks from real developer sessions | 55.5% | 57.8% |
| FrontierCode 1.1 | Whether code changes would be merged | 52.1% (Xhigh) | 54.4% |
| Humanity’s Last Exam (with tools) | Hard multi-subject reasoning | 64.5% | 67.7% |
| Chartography (no tools) | Reading charts | 61.6% | 64.4% |
| Terminal-Bench 4.0 | Multi-step command-line work | 70.6% | 66.4% (Opus at Xhigh) |
Source: Anthropic’s Sonnet 5.5 announcement. Sonnet scored 46.2% on FrontierCode at max effort; Anthropic attributes the drop to timeouts and extra edits.
No percentage gap exceeds about three points, and Sonnet’s one win, Terminal-Bench, compares it against Opus at its highest setting. Anthropic still cautions that benchmarks capture one facet of a model and that Opus 5.5 remains clearly stronger at complex, open-ended work needing sustained judgment. In its Opus announcement it also says benchmark margins have become a less reliable guide to real-world differences.
Independent testing points the same way. CodeRabbit, which sells AI code review, tested Sonnet 5.5 on 13 hard known-bug cases and compared it with its earlier Opus 5.5 results: Sonnet 5.5 caught 6, while Opus 5.5 caught 8 at standard settings and 10 at max. The sample is small and CodeRabbit has a commercial interest, but Sonnet 5.5 did finish reviews in about half the time of Sonnet 5 (6:33 against 13:31 minutes on 44 pull requests).
Which model should you use for writing, slides and research?
Use Sonnet 5.5 for everyday writing, slides and spreadsheets. Switch to Opus 5.5 for long research, tricky analysis, or any task where mistakes are costly.
| Task | Start with | Why |
|---|---|---|
| Blog drafts, emails, social copy | Sonnet 5.5 | Faster and cheaper, and Anthropic says both models write more clearly than the last generation |
| Slides and spreadsheets from a template | Sonnet 5.5 | Anthropic names documents, slides and spreadsheets as a strength |
| Quick edits, summaries, support replies | Sonnet 5.5 (low or medium effort) | Cheapest per task at matched effort |
| Sourced research or competitor analysis | Opus 5.5 | Anthropic’s test: 16 of 18 reports had no invented figures |
| Financial or data analysis | Opus 5.5 | Walleye Capital says it caught an error in its own test instructions |
| Long projects left running | Opus 5.5 | Built for sprawling, judgment-heavy work |
On slides, Anthropic gave Sonnet 5.5 a public company’s earnings materials and a template, and two experts judged its first 10-slide draft ready to send as is. On support work, “Tickets were processed 20% faster,” says Abhinay Kathuria, Director of AI at Zendesk.
For research, Anthropic asked Opus 5.5 to write company quarterly-performance reports while an automated grader checked every figure, and 16 of 18 reports passed with no invented figure or quote. That is Anthropic’s own internal test, so verify numbers yourself; our guide to why AI makes up fake citations explains why. On writing quality, “It writes like a good colleague,” says John Ruelas, Staff Software Engineer at Ramp.
Builders care about efficiency too. Lovable’s CTO reported in Anthropic’s launch notes that in its coding evaluations Sonnet 5.5 needed about a third fewer tool calls, and that Opus 5.5 finished builds in a third to half fewer steps. If you want to try building an app without code, Lovable has a free plan, and Replit is a solid alternative; see our Replit vs Lovable comparison. I have not confirmed which Claude models either tool lets you select, so check their settings.
My rule of thumb, not a tested result: draft and iterate on Sonnet 5.5, then hand the final check on anything sourced or high stakes to Opus 5.5. Clearer instructions help either model, so see our guide to writing better AI prompts.
Are there safety or availability differences?
Both models are available on all major platforms and carry cybersecurity safeguards. Riskier security requests fall back to an older model rather than failing outright.
Anthropic says both models are on the Claude Platform, Amazon Web Services, Google Cloud and Microsoft Azure, and both offer zero data retention. For security requests, higher-risk work on Sonnet 5.5 falls back to Sonnet 5, and most cybersecurity tasks on Opus 5.5 are rerouted to Opus 4.8. Routine bug fixing is unaffected on both.
On alignment, Anthropic reports that Opus 5.5 scored best of any model it has tested on its automated behavioral audit, and attempted to cross containment boundaries about 85% less often than Opus 5 in a new test. Sonnet 5.5 improves on or matches Sonnet 5 on most measures, while Opus 5.5 still performs slightly better overall. Opus 5.5 also ships with watermarking measures for the EU AI Act.
Frequently Asked Questions
Is Sonnet 5.5 better than Opus 5.5?
Not overall. Sonnet 5.5 is within roughly three points of Opus 5.5 on most of Anthropic’s benchmarks and beats it on Terminal-Bench 4.0 (70.6% against 66.4%, with Opus at its highest setting). But Anthropic says Opus 5.5 remains clearly stronger on complex, open-ended work, and Artificial Analysis scores it higher (58 against 56 at max effort).
Is Opus 5.5 worth twice the price?
Not automatically. Opus 5.5 costs double per token, but Anthropic says it uses fewer tokens and costs 40% less than Opus 5 on typical workloads. On Artificial Analysis data, Opus 5.5 at low effort matched Sonnet 5.5 at medium on both score and cost. For routine tasks Sonnet is cheaper; for hard ones Opus is often not much dearer.
Which model is faster?
Sonnet 5.5 streams text faster: Artificial Analysis measured 138 tokens per second at max effort against 93 for Opus 5.5. But speed per task depends on how much the model thinks. At max effort Sonnet 5.5 took about 868 seconds per task against 807 for Opus 5.5, partly because it wrote more tokens along the way.
Can I use both models together?
Yes. MyClaw’s summary of Anthropic’s docs describes two patterns: Sonnet 5.5 does the work and asks Opus 5.5 for advice on hard decisions, or Opus 5.5 plans the job and hands routine subtasks to Sonnet 5.5. For everyday users the same idea works manually: draft with Sonnet, then check important claims with Opus.
When will Claude Haiku 5.5 arrive?
Anthropic says Claude Haiku 5.5 will join the Claude 5.5 family in the coming weeks and is built for high-volume, cost-sensitive applications. No release date or pricing appears on the launch pages, so this article will be updated when it ships.
Related reading:
- ChatGPT vs Claude vs Gemini: which is best for beginners
- AI writing tools: a beginner’s guide for marketers
- Free AI tools for beginners
- How to make an app with AI
