Claude Sonnet 5.5 is Anthropic’s newest mid-tier AI model, released on September 28, 2026. It costs the same as Sonnet 5 ($2 per million input tokens and $10 per million output tokens), runs 30%+ faster, and lands close to the flagship Opus 5.5 on many coding and office-work tests. If you build with Claude or use it every day, this is now the default “workhorse” model to know.
Below, you’ll find the full pricing, the benchmark numbers that matter, where you can use it, and when it still makes sense to pay for Opus 5.5 instead.
Claude Sonnet 5.5 at a Glance
| Detail | Claude Sonnet 5.5 |
|---|---|
| Release date | September 28, 2026 |
| Model family | Claude 5.5 (second model after Opus 5.5) |
| API model ID | claude-sonnet-5-5 |
| Context window | 1M tokens |
| Max output | 128K tokens (300K via Batch API, beta) |
| Knowledge cutoff | June 2026 |
| Input / output price | $2 / $10 per million tokens |
| Cache reads | $0.20 per million tokens |
| Default effort | Medium in Claude apps, High on the Claude Platform |
| Platforms | Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry, Claude Platform on AWS |
What Is Claude Sonnet 5.5?
Sonnet 5.5 is the second model in Anthropic’s Claude 5.5 family, after Opus 5.5. Anthropic positions it as the faster, cheaper partner to Opus. Opus handles complex work that needs careful judgment, while Sonnet targets well-scoped everyday jobs.
Think of tasks like fixing bugs, finishing features, and producing polished documents, slides and spreadsheets. Anthropic also says the model has a sharp eye for design, so it adds polish to user interfaces and follows slide templates closely.
A third model, Claude Haiku 5.5, is due “in the coming weeks” for high-volume, low-cost apps. So Sonnet 5.5 sits in the middle of the lineup, just as earlier Sonnet models did.
Claude Sonnet 5.5 Pricing Explained
The headline: the price per token did not change. You pay exactly what you paid for Sonnet 5. The savings come from the model needing fewer tokens to finish the same task.
| Price per 1M tokens | Claude Sonnet 5.5 | Claude Opus 5.5 |
|---|---|---|
| Input tokens | $2 | $4 |
| Output tokens | $10 | $20 |
| Cache writes (5 min) | $2.50 | $5 |
| Cache reads | $0.20 | $0.20 |
| Batch API | 50% off input and output | — |
Anthropic says Sonnet 5.5 costs up to 30% less per task than Sonnet 5 in its own testing. The Claude Platform docs also list a 1-hour cache write at $4 per million tokens and a 50% Batch API discount.
The catch: high effort can burn tokens
Here’s the part most launch coverage skips. Independent testers at Artificial Analysis found that at its maximum effort setting, Sonnet 5.5 used about 193,000 output tokens per task on their Intelligence Index. That’s the highest token use they’ve measured.
At that setting, they estimate the real cost per task at about $7.60, roughly 50% more than Sonnet 5. So the “cheaper” claim depends heavily on which effort level you choose. At Low or Medium effort, Anthropic’s own charts show Sonnet 5.5 beating Sonnet 5’s best score for about a tenth of the cost per task.
Bottom line: if you care about your bill, start at Medium effort and only raise it when results fall short.
Claude Sonnet 5.5 Benchmarks
Anthropic published a long list of scores. These are the ones that tell you the most, with Sonnet 5 and Opus 5.5 for context.
| Benchmark | Sonnet 5.5 | Sonnet 5 | Opus 5.5 |
|---|---|---|---|
| Terminal-Bench 4.0 (agentic coding) | 70.6% | 10.3% | 66.4% |
| CursorBench 4.0 (real coding sessions) | 55.5% | 34.1% | 57.8% |
| FrontierCode 1.1 Main | 46.2% (Max) | 42.4% | 54.4% |
| GDPval-AA v2.1 (real-world work) | 1844 | 1449 | 1846 |
| Humanity’s Last Exam (with tools) | 64.5% | 54.9% | 67.7% |
| OSWorld 2.1 (computer use) | 80.1% | 57.0% | 81.8% |
| Chartography (chart reading, no tools) | 61.6% | 15.6% | 64.4% |
A few things stand out:
- Coding jumped the most. On Terminal-Bench 4.0, Sonnet 5.5 scored 70.6%, above Opus 5.5’s 66.4% at its best setting.
- Office work is nearly level with Opus. On GDPval-AA, which covers tasks across 44 occupations, it’s just two points behind Opus 5.5.
- Chart reading improved hugely, from 15.6% to 61.6%.
What independent testers found
Outside testing broadly backs this up, with some caveats. Artificial Analysis ranks Sonnet 5.5 #2 on its Intelligence Index with a score of 56, behind only Opus 5.5 at max effort. Vals.ai ranks it #2 of 43 models on its Vals Index at 67.04%.
But Artificial Analysis also found it lags Opus 5.5 on factual knowledge (54% versus 66% accuracy). And Anthropic itself says Opus 5.5 “remains clearly stronger” at complex, open-ended work.
Early Tester Results in Real Products
Benchmarks are useful, but you probably care more about real workloads. Anthropic shared results from companies that tested Sonnet 5.5 before launch.
| Company | What they measured | Result |
|---|---|---|
| Zendesk | Support ticket handling | Tickets processed 20% faster |
| Box | Document work vs Sonnet 5 | 2.4x faster, 12% fewer total tokens |
| Balyasny Asset Management | 2,441 finance tasks | About 121k tokens per answer vs 497k for Sonnet 5 |
| Base44 | 118 real app builds | 3.6 iterations per build vs 7.7 for Opus 5 |
| Slack | Slackbot evals | About 14% fewer output tokens |
| Unity | Multi-step Unity Editor tasks | 90% of tasks completed |
The common thread is efficiency. Teams saw fewer steps, fewer tokens and faster answers without changing their prompts much. Keep in mind these are vendor-selected quotes, so test your own workload before switching everything over.
What’s New Compared With Sonnet 5
If you’re upgrading, here’s what actually changes for you day to day.
- Speed: output is 30%+ faster, making it Anthropic’s fastest Sonnet model yet.
- Efficiency: testers saw fewer tool calls and fewer steps per task. Lovable reported about a third fewer tool calls on its coding evals.
- Writing: Anthropic says it writes more clearly, and early testers called it a better collaborator.
- Vision: it’s the first Sonnet model to beat Pokémon Red using only screenshots.
- Safety guardrails: it’s the first Sonnet launched with cybersecurity safeguards like those on Opus 5.5. Higher-risk security tasks visibly fall back to Sonnet 5.
Breaking changes developers should know
The Claude Platform docs list five breaking changes from Sonnet 5. The big one: if you ran Sonnet with thinking off, you now need the new between_tools setting, which keeps up-front thinking off.
Forced tool use now returns an error, and thinking blocks are tied to the model and conversation. Check Anthropic’s migration guide before you switch production traffic.
Sonnet 5.5 vs Opus 5.5: Which Should You Use?
This is the real decision for most teams. Here’s a simple way to choose.
| If you need… | Pick | Why |
|---|---|---|
| Bug fixes, features, routine code review | Sonnet 5.5 | Near-Opus coding scores at half the token price |
| Docs, slides, spreadsheets | Sonnet 5.5 | Strong design sense and template following |
| High-volume agents and support bots | Sonnet 5.5 | Faster output, fewer steps per task |
| Architecture and open-ended planning | Opus 5.5 | Anthropic says Opus stays stronger on sustained judgment |
| Fact-heavy research answers | Opus 5.5 | Higher factual accuracy in independent tests |
A smart pattern is to pair them. Let Opus 5.5 set the plan or architecture, then hand implementation to Sonnet 5.5. AWS recommends this same split in its launch post, and one early tester described exactly that workflow for game development.
If you’re comparing across vendors, our breakdown of Gemini 4 Argon and our Grok vs ChatGPT comparison cover the main rivals. For OpenAI’s latest launches, see our OpenAI DevDay 2026 roundup.
How to Access Claude Sonnet 5.5
You can use the model in a few ways, depending on whether you’re a regular user or a developer.
- In the Claude apps: Sonnet 5.5 runs at Medium effort by default. Developer Simon Willison noted on launch day that it now powers Claude.ai’s free tier.
- Through the Claude API: call the model ID claude-sonnet-5-5. The platform default effort is High.
- On Amazon Bedrock: use anthropic.claude-sonnet-5-5 through the Global cross-region inference profile.
- On Google Cloud or Microsoft Foundry: the model ID is claude-sonnet-5-5.
- For sensitive data: Anthropic says it’s available with zero data retention, like Opus 5.5.
Tips to Get the Best Results
These small changes can save you money and frustration.
- Start at Medium effort. It’s the app default for a reason, and it’s where the cost advantage is clearest.
- Avoid Max effort for routine jobs. Anthropic’s own footnote notes Sonnet 5.5 scored lower at Max than Xhigh on FrontierCode, partly from extra out-of-scope edits.
- Use prompt caching. Cache reads cost just $0.20 per million tokens.
- Batch non-urgent work. The Batch API halves token prices.
- Keep prompts simple. Several testers said it needs less prescriptive prompting than Sonnet 5.
If you’re new to coding with AI agents, our guide to vibe coding explains the basics.
Is Claude Sonnet 5.5 Worth It?
For most people, yes. You get a big jump in coding, computer use and chart reading at the same per-token price. Upgrading from Sonnet 5 is close to a free win, as long as you handle the breaking changes.
Just watch your effort settings. At Max effort, token use can wipe out the savings. And for the hardest, most open-ended work, Opus 5.5 is still the stronger pick.
Source: Anthropic – Introducing Claude Sonnet 5.5.
Frequently Asked Questions
Anthropic released Claude Sonnet 5.5 on September 28, 2026. It is available on the Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry and Claude Platform on AWS.
It costs $2 per million input tokens and $10 per million output tokens, the same as Sonnet 5. Cache reads are $0.20 per million tokens, and the Batch API cuts prices by 50%.
Usually, yes. Anthropic says it costs up to 30% less per task because it needs fewer tokens. At maximum effort, though, independent testing found it can cost about 50% more per task.
Not overall. It matches or beats Opus 5.5 on some coding tests, like Terminal-Bench 4.0, but Opus 5.5 remains stronger on complex, open-ended work and factual knowledge.
Sonnet 5.5 supports a 1 million token context window and up to 128K output tokens, or 300K output tokens through the Batch API beta.
Developer Simon Willison reported that Sonnet 5.5 now powers the free tier of Claude.ai. Check your plan page in the Claude app to confirm which models you can pick.
Anthropic says Haiku 5.5 will join the Claude 5.5 family “in the coming weeks” but has not given an exact date.
