What is Claude Opus 5.5? Anthropic's Workhorse Model With Near-Fable 5.1 Performance at a Lower Price
Claude Opus 5.5 is Anthropic's large language model released on September 22, 2026, built for long-running coding and knowledge work. Here is what it is, what it costs, and what to watch for.
In this article
Claude Opus 5.5 is a large language model Anthropic released on September 22, 2026, and the first member of the Claude 5.5 family. Anthropic positions it for long-running agentic coding and knowledge work.
Two things matter for most readers. It is cheaper than the previous Opus 5, and Anthropic says it performs close to the higher-tier Fable 5.1 on most work. The goal is to make near-top-tier AI affordable for more people.
If Fable 5.1 is the star chef you call for the hardest dishes, Opus 5.5 is the reliable head chef who handles most of the menu quickly and consistently.
The short version
Claude Opus 5.5 is the model Anthropic suggests starting with for most workloads. The company says it costs about 40% less than Opus 5 and generates output over 30% faster. Those are Anthropic's claims, so test them on your own tasks.
What problem does it solve?
Complex jobs, like large code migrations, multi-day coding sessions, or sorting through piles of documents, need a model that stays on track for a long time and checks its own work. The strongest models tend to be expensive, which keeps many teams from using them at scale.
Anthropic's answer is a lower price with performance near the tier above. The official model overview recommends starting with Opus 5.5 and moving to Fable 5.1 only if your evaluations at higher effort still fall short. Models overview
Key features
1. Lower price, faster output
| Item | Opus 5.5 | Opus 5 |
|---|---|---|
| Input (per million tokens) | $4 | $5 |
| Output (per million tokens) | $20 | $25 |
| Cache reads | $0.20 | $0.50 |
A token is the unit models use to process text. Cache reads are discounted prices for reused content. Anthropic says Opus 5.5 costs about 40% less than Opus 5 on typical workloads. A fast mode runs up to roughly 2.5x faster at $8 input and $40 output. Anthropic announcement
2. Published benchmark results
Anthropic compared Opus 5.5 with Fable 5.1, Opus 5, and OpenAI's GPT-6 Astra. Selected results:
| Benchmark | Opus 5.5 | Fable 5.1 | Opus 5 | GPT-6 Astra |
|---|---|---|---|---|
| Terminal-Bench 4.0 (terminal tasks) | 66.4% | 55.8% | 52.3% | 57.9% |
| FrontierCode v1.1 | 54.4% | 50.3% | 48.0% | 53.3% |
| OSWorld 2.1 (computer use, partial) | 81.8% | 80.7% | 74.0% | not reported |
| Humanity's Last Exam (with tools) | 67.7% | 65.6% | 63.6% | 57.2% |
These are vendor-run results. Anthropic itself cautions that at this capability level, benchmark margins are a less reliable guide to real-world differences, and that safeguards may have lowered scores on some tasks. Also, GPT-6 Astra scored higher on Terminal-Bench-Science 0.1 and AutomationBench, so this is not a clean sweep.
3. Safety and control
Anthropic says Opus 5.5 scored best of any model on its automated behavioral audit of nearly 2,000 scenarios, and is less likely to take hard-to-reverse actions or act outside its bounds. It also claims better resistance than Opus 5 to prompt injection (hidden instructions in web pages or documents that try to steer an AI).
In cybersecurity and biology it uses safeguards similar to Fable 5.1, and most cybersecurity tasks are rerouted to Opus 4.8. Anthropic also notes the model often suspects it is being tested, which limits how well tests predict real-world behavior.
4. Key specs
| Item | Detail |
|---|---|
| API model ID | claude-opus-5-5 |
| Context window | 1M tokens |
| Max output | 128K tokens |
| Modalities | Text and image in; text out |
| Reliable knowledge cutoff | June 2026 |
| Thinking | Adaptive, cannot be turned off; default effort medium |
Adaptive thinking lets the model decide how long to think, steered by an effort setting. Specs come from the official overview; check it before relying on them.
How does it compare with the rest of the Claude family?
| Model | Official positioning | Price (input / output per million tokens) | Latency |
|---|---|---|---|
| Fable 5.1 | Demanding reasoning and long-horizon agentic work | $10 / $50 | Slower |
| Opus 5.5 | Long-running agentic coding and knowledge work | $4 / $20 | Moderate |
| Sonnet 5.5 | Best combination of speed and intelligence | $2 / $10 | Fast |
| Haiku 5.5 | High-volume, latency-sensitive tasks like classification, extraction, routing | From $0.10 / $0.50 | Fastest |
What non-engineers should know
- What it's good at: Customer feedback Anthropic cites mentions overnight coding runs and large migrations, plus clearer writing with key points up front. This is curated company-reported feedback.
- Subscribers: Five-hour usage limits were raised on Pro, Max, Team, and seat-based Enterprise plans, with a rate-limit reset that can be saved for later.
- Where to use it: Claude API, Amazon Bedrock, Google Cloud, and Microsoft Foundry.
Who is it for?
- Teams running long coding workflows or large document jobs who care about cost.
- Developers building AI agents who want a strong default model to tune up or down from.
- Writers and analysts who value clear, easy-to-review output.
Who might skip it?
- Teams with extremely hard tasks who will pay more for peak performance should compare Fable 5.1.
- High-volume simple classification or extraction usually fits Sonnet 5.5 or Haiku 5.5 better.
- Apps that need thinking turned off, which Opus 5.5 does not allow.
- Cybersecurity or biology research, where some tasks are restricted or rerouted and verification programs may apply.
How to get started
Check your Claude plan's model picker for Opus 5.5. Developers can call it by model ID:
curl https://api.anthropic.com/v1/messages \
-H "x-api-key: $ANTHROPIC_API_KEY" \
-H "anthropic-version: 2023-06-01" \
-H "content-type: application/json" \
-d '{
"model": "claude-opus-5-5",
"max_tokens": 1024,
"messages": [{"role": "user", "content": "Summarize the three key points of this document."}]
}'
Start with a real task whose answer you can judge, and record completion, correction time, and total cost before deciding to adopt it.
Our take
The most notable thing about Opus 5.5 is the price cut itself. The bar for using top-tier models is dropping, and competition is shifting from "who is strongest" to "who finishes work reliably at a sensible cost."
The second signal is safety. Anthropic leads with behavioral audits, injection resistance, and safeguards, suggesting that as AI works more autonomously, "doesn't overstep" becomes a selling point.
Still, every score and cost figure here comes from the vendor, and testing conditions differ between labs. A small side-by-side test on your own tasks beats any leaderboard.
Sources
- Anthropic: Introducing Claude Opus 5.5
- Anthropic: Models overview
- TechCrunch: Anthropic releases Opus 5.5 with lower prices and Fable-level performance
- Checked on 2026-10-09. Products and prices may change; usage tips and commentary are our own.