What Is Claude Opus 5.5? Features, Access & Use Cases

What is Claude Opus 5.5? It's Anthropic's newest Opus model, and it's now the one Anthropic tells most people to start with. Anthropic released Opus 5.5 on September 22, 2026 as the first model in its Claude 5.5 family.

Opus 5.5 is designed for jobs that take many steps, like building software, working through research, or turning messy information into finished documents. Compared with the Opus 5 model it replaces, it's also cheaper and faster.

This guide explains what changed, what people use it for, where you can get it, and the limits worth knowing before you rely on it.

What is Claude Opus 5.5? Anthropic's recommended starting model for long, multi-step work

On price, Claude Opus 5.5 sits between Anthropic's faster Sonnet and Haiku models and the pricier Fable 5.1, but it's the model Anthropic points most people to first. Anthropic's model guidance now says to start with Opus 5.5 for most workloads. Fable 5.1 is for the most demanding reasoning, or for tasks where Opus at higher effort still falls short.

That makes Opus 5.5 the everyday workhorse of the lineup. Its core job is long-running agentic coding and knowledge work. That means tasks where the model plans, uses tools, checks its own progress, and keeps going over many steps.

Table 1: Claude Opus 5.5 key facts, as of September 2026. Sources: Anthropic launch post and Claude Platform documentation.

Anthropic has said Claude Sonnet 5.5 and Claude Haiku 5.5 will follow in the coming weeks, bringing similar improvements to its smaller, cheaper models.

Six things changed from Opus 5

Opus 5.5 replaces Opus 5, which launched in July 2026. The changes add up to a model that's more capable, cheaper to run, and easier to read.

1. It thinks on every request: Opus 5 could skip its reasoning step, but Opus 5.5 always reasons before answering. An effort setting controls how hard it thinks, and the default dropped from high to medium.
2. It costs less per token: input and output prices fell 20%, to $4 and $20 per million tokens, and reading from the prompt cache got 60% cheaper.
3. It uses fewer tokens per task: in Anthropic's tests, the lower prices plus leaner work made typical workloads about 40% cheaper to run at default settings.
4. It's faster: Anthropic says it generates output more than 30% faster than Opus 5.
5. It writes more clearly: writing was one of the most common areas of feedback on Opus 5. Opus 5.5 puts the key point first, uses less jargon, and follows the writing rules you give it.
6. It has stronger safeguards: it's the first Opus model with a similar class of safeguards to Fable 5.1, covering cybersecurity, biology, and model distillation (attempts to copy its reasoning). Some protected requests are handled by fallback models.

For the full upgrade decision, including every benchmark change and what breaks in existing code, see our Opus 5.5 vs Opus 5 comparison. [INTERNAL LINK PLACEHOLDER: link "Opus 5.5 vs Opus 5 comparison" to the Opus 5.5 vs Opus 5 article once it's live]

What Claude Opus 5.5 is used for

Claude Opus 5.5 is used for work that takes many steps and has to come out right: building and fixing software, research and analysis, and business documents. The launch examples show where it helps most.

• Coding and software projects: in one early test, Opus 5.5 audited and fixed a 200,000-line codebase in under three hours. The same job took Opus 5 more than 20 hours and 2.5 times as many tokens.
• Research reports: each model wrote a quarterly earnings report, with a grader checking every figure and quote. Across effort settings, 16 of 18 Opus 5.5 reports passed, and none from Opus 5 did.
• Financial and business analysis: Opus 5.5 built a merger model and an executive presentation in 63 minutes, against 93 for Opus 5, at half the cost.
• Reading charts and screenshots: it scored 89.0% on Chartography, a chart-reading benchmark in Anthropic's launch table, up from 83.4% for Opus 5. That helps with dashboards, reports, and scanned documents.

These are Anthropic's own tests and early-tester reports, so treat them as strong signals rather than guarantees. For everyday chat, drafting, or simple questions, a lighter model like Sonnet is often enough.

How good Opus 5.5 is: top of most benchmarks, with independent checks

Opus 5.5 is among the leading models for agentic coding and professional knowledge work. On Anthropic's own launch table, it scored 66.4% on Terminal-Bench 4.0, a test of multi-step coding in a terminal. Fable 5.1 scored 55.8%, and GPT-6 Astra an OpenAI-reported 57.9% at a different effort setting.

Independent testing backs up the overall picture. At max effort, Opus 5.5 took the top spot on Artificial Analysis's Intelligence Index with a score of 58, as of September 2026. The index runs every model through the same set of tests.

A code-quality evaluation from Sonar adds a different angle. Sonar tested a pre-release build of Opus 5.5 at high effort on Java tasks. Compared with Opus 5, the new model wrote 27.5% less code at a similar pass rate (87.7% vs 88.6%). Its total code-quality findings fell 42%.

Our Opus 5.5 benchmarks breakdown covers every score, what each benchmark measures, and which results are independently verified.

How much Claude Opus 5.5 costs

On Anthropic's API, Opus 5.5 costs $4 per million input tokens and $20 per million output tokens. On Claude's subscription plans, it's included from the $20-a-month Pro plan upward, subject to each plan's usage limits. Batch jobs cost half as much, and a faster mode costs double.

Our Claude Opus 5.5 pricing guide covers the full rate card, the plan comparison, and what a real task costs at each effort level.

Where you can use Claude Opus 5.5

Opus 5.5 is available on Anthropic's API, the major cloud platforms, and paid Claude plans, but Claude's Free plan doesn't include it. Developer tools added it the same week it launched.

Table 2: Where Claude Opus 5.5 is available, as of September 2026.

Plan prices start at $20 a month for Pro, or $17 a month billed annually, according to Claude's plans page. Max starts at $100 a month for heavier use. In GitHub Copilot, Opus 5.5 is billed at list pricing under usage-based billing and is rolling out gradually across its supported editors and apps.

How to get good results from Opus 5.5

The biggest setting to understand is effort. Opus 5.5 always thinks before answering, and the effort level decides how much. Medium is the default, and Anthropic's guidance is to start there and test lower and higher levels on your own work.

• Keep medium for most tasks: it's the default for a reason, balancing quality, speed, and cost.
• Raise effort for hard, multi-step problems: high or xhigh can help with complex coding or analysis, but costs more.
• Use max sparingly: it produces the best scores but uses far more tokens, which can wipe out the model's price advantage.
• Leave room for thinking: at a given effort level, Opus 5.5 thinks more per turn than Opus 5, so developers should set output limits with that in mind.

Prompts written for Opus 5 should work well without changes, according to Anthropic. Developers calling the API directly should check Anthropic's what's new guide, because a few request settings that worked on Opus 5 now return errors.

Where Opus 5.5 fits against Opus 5 and Fable 5.1

Against Opus 5, the answer is simple: Opus 5.5 scores higher on every benchmark in Anthropic's launch table and costs less. Opus 5 is now a legacy model, still available until at least July 2027, so there's no rush for anyone who depends on it.

Against Fable 5.1, it's closer than the prices suggest. Fable 5.1 costs $10 and $50 per million tokens, two and a half times as much, yet Opus 5.5 scored higher on every benchmark in Anthropic's launch table. The real-world gap is also narrower than those scores suggest, according to Anthropic. Fable 5.1 still makes sense for very hard, open-ended problems. For that decision, see our Fable 5.1 vs Opus 5.5 comparison.

Limits worth knowing before you rely on Opus 5.5

Opus 5.5 is a big step forward, but it isn't flawless, and a few behaviors can surprise new users.

• A few higher-risk requests go to other models: most requests never trigger a fallback, according to Anthropic's help center. Flagged offensive security work, like exploit generation or penetration testing, moves to Claude Opus 4.8. Dual-use biology and some frontier AI development requests move to Claude Opus 5. You'll see a notice when the model switches, and secure coding, including scanning your own code for vulnerabilities, stays on Opus 5.5. Vetted organizations can apply to Anthropic's Life Sciences Verification Program.
• Max effort can cost more than you expect: the extra thinking can cancel out the lower token prices. The savings show up most at default settings.
• Its code still needs checking: in Sonar's pre-release Java evaluation, it produced fewer total issues but a 12% higher bug rate per line, driven mostly by concurrency problems. Roughly one in eight of its solutions failed Sonar's test-backed tasks.
• Its text is watermarked: Opus 5.5 applies text watermarking to its output. GitHub notes this doesn't change meaning or quality and adds no tokens or cost.

None of these is a reason to avoid it. They're reasons to keep a person reviewing important work, and to test it on your own tasks before switching everything over.

Build with Claude Opus 5.5 on Emergent

So what is Claude Opus 5.5? It's Anthropic's recommended starting model for serious, multi-step work: stronger than Opus 5, cheaper to run, faster, and clearer in how it writes. Its best uses are long coding projects, research, analysis, and business documents, with a person still checking the results.

You don't need to write code to use it for building. Opus 5.5 is live on Emergent, where you describe the app or tool you want and pick the model when you start a project. In our own builds, the main building agent used 18% fewer credits on Opus 5.5 than on Opus 5. If your app needs its own AI features, the Universal LLM Key gives it one credential for Claude, GPT, and Gemini.

Start Building on Emergent.