Claude Opus 5.5 matches Fable 5.1 performance at lower cost and promises less "Claudish" writing

Claude Opus 5.5 matches Fable 5.1 performance at lower cost and promises less "Claudish" writing

Matthias Bastian View the LinkedIn Profile of Matthias Bastian
Sep 22, 2026

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Update – Sep 22, 2026

• Added Artificial Analysis benchmark results

Anthropic is launching Claude Opus 5.5, the first model in a new family. The company says it delivers Claude Fable 5.1-level performance while costing significantly less and running faster than its predecessor.

According to Anthropic, Opus 5.5 matches Claude Fable 5.1 "on most tasks" while costing about 40 percent less to run than Opus 5. Claude Sonnet 5.5 and Haiku 5.5 are expected in the coming weeks, with similar gains in performance, efficiency, and safety. Anthropic's benchmarks show the new Opus model ahead of both Fable 5.1 and OpenAI's much more expensive GPT-6 Astra on most tasks.

Anthropic says the new series primarily addresses customer feedback on cost, efficiency, and communication quality, particularly in financial services, law, and software development.

Lower prices and token usage cut operating costs

Anthropic prices Opus 5.5 at $4 per million input tokens and $20 per million output tokens, down from $5 and $25, respectively, for Opus 5. That's a 20 percent cut in token prices. The company also reduced cache read costs by 60 percent.

Anthropic says total operating costs, which account for both token prices and token usage, should be about 40 percent lower than Opus 5's. The model uses fewer tokens and generates output more than 30 percent faster.

Five-hour usage limits for subscribers will increase by 20 percent. With the model's lower costs, Anthropic says those limits stretch 25 percent further overall. Users can also save a limit reset for when they need it most.

Anthropic is using coding benchmarks to make its case on price and performance. On FrontierCode, the company says Opus 5.5 beats OpenAI's GPT-6 Astra at about 20 percent of the cost per task. On Terminal-Bench 4.0, it claims the same performance as Astra at 40 percent of the cost. On CursorBench, it says Opus 5.5 beats GPT-5.6 Sol by 11 points at one-third of the cost.

The price cut is a response to pressure from OpenAI and especially Chinese AI models, which offer lower performance but cost a fraction as much.

Anthropic promises less "Claudish"

Opus 5.5 is also supposed to communicate more naturally than earlier models. Anthropic says it puts the most important information first, uses less jargon, and follows writing instructions more closely. Early testers described its writing as clearer and easier to understand, which Anthropic says makes it a better partner for long work sessions. Current Claude models have drawn plenty of criticism for their formulaic, convoluted writing, sometimes called "Claudish".

Opus 5.5 is also the first Opus model with safeguards for cybersecurity, biology, and frontier LLM development that match those of Fable 5.1. When those safeguards kick in, Anthropic says requests are transparently routed to another model.

Users can still find and fix bugs in their code, but most cybersecurity tasks will go to the older Opus 4.8. Requests flagged by classifiers for biology or frontier LLM development will go to Opus 5.

Verified organizations can apply to use the model for biological research through the Life Sciences Verification Program. Anthropic plans to extend its existing Cyber Verification Program to Opus 5.5 in the coming weeks.

Claude Opus 5.5 is available now on all platforms, including Amazon Web Services, Google Cloud, and Microsoft Azure. Developers using the Claude Platform can access it with the model ID claude-opus-5-5.

Anthropic calls for higher safety standards as models become more capable

Anthropic plans to screen reinforcement learning environments more strictly. The company says flawed training environments are a major source of misaligned model behavior. It's also working on better alignment rewards, automated ways to create safety training scenarios, and stronger safety and monitoring measures.

AI labs are debating how quickly to release more capable models. OpenAI recently called for international standards for AI systems that could improve themselves, while several researchers have publicly urged labs to slow releases until alignment methods catch up. Anthropic is taking a similar position, calling for a higher safety standard for models that could automate AI research entirely. The company says public policy should have a greater role in setting that standard. External organizations Frontier Design and METR tested Opus 5.5 before its release.

New restrictions target distillation and support EU AI Act compliance

Anthropic is also introducing measures against what it calls distillation attacks. The company says attackers use thousands of fake accounts to extract a model's capabilities at an industrial scale and build highly capable models without its safeguards. Anthropic cites a September 2026 threat report documenting illegal distillation activity it has detected and stopped so far.

Opus 5.5 launches with "Preserved Thinking," an anti-distillation measure first introduced with Fable 5.1. It prevents API users from editing Claude's prior context to extract its reasoning. The measure applies to Fable 5.1 and Opus 5.5 for API accounts created on or after August 31, 2026.

Opus 5.5 also includes watermarking measures to comply with the EU AI Act. The model can no longer run with "Thinking" mode disabled and it is available with Zero Data Retention.

Artificial Analysis puts Opus 5.5 at the top of its intelligence index

Independent platform Artificial Analysis confirms Opus 5.5's strong showing. At max effort, the model scores 58 on the Artificial Analysis Intelligence Index, the highest ever and several points above the previous leader. It leads six of ten evaluations, including Humanity's Last Exam at 61.4 percent (previous best: 59.1 percent, Fable 5.1) and SciCode at 66.9 percent (63.1 percent, also Fable 5.1). On Terminal-Bench 4.0, Opus 5.5 hits 59.6 percent, tying GPT-6 Astra and beating Opus 5 by 11 points.

Artificial Analysis says Opus 5.5 brings Anthropic to parity with GPT-6 Astra on Terminal-Bench 4.0 and AutomationBench-AA while extending its lead in agentic knowledge work. On the private AA-Briefcase benchmark, Opus 5.5 hits an Elo of 1,822, up 143 from Fable 5.1, marking the first time an Anthropic model has beaten GPT-5.6 Sol on presentation quality. On GDPval-AA, an OpenAI benchmark for real-world white-collar work, Opus 5.5 outperforms Astra on every reasoning mode except low.

Artificial Analysis does flag an efficiency tradeoff. At max effort, Opus 5.5 burns about 119,000 output tokens per task, far more than Opus 5 (73,000), Fable 5.1 (78,000), or GPT-6 Astra (27,000). Lower token prices keep its cost per task in line with Opus 5, but not cheaper. But four of five Opus 5.5 effort levels land on the Pareto frontier, matching or beating every other model above 50 on the index for cost per task.

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Source: Anthropic | Artificial Analysis