Introduction to Claude Opus

Claude Opus is Anthropic's flagship line of AI models, built for complex, high-stakes work. The latest release is Claude Opus 5.5 (September 22, 2026), the first model in the Claude 5.5 family. Anthropic says it performs at the level of its top-tier Claude Fable 5.1 on most work and costs 40% less to run than Opus 5.

Why "Opus"?

The name "Opus" means a masterpiece or a work of significant scale. In the Claude family it's the flagship, the model most people choose for serious work:

Haiku: Fastest, most cost-effective.
Sonnet: Balanced performance and speed.
Opus: Frontier intelligence at a practical price.
Fable: Anthropic's highest tier, with a higher price, for the very hardest problems.

Key Capabilities

1. State-of-the-Art Agentic Coding

Opus 5.5 scores 66.4% on Terminal-Bench 4.0 and 54.4% on FrontierCode v1.1, leading OpenAI's GPT-6 Astra (57.9% and 53.3%) on both. It also posts 81.8% on OSWorld 2.1 for computer use.

2. Knowledge Work

On GDPval-AA v2.1, a test of real-world professional tasks, Opus 5.5 scores 1846 Elo, ahead of Fable 5.1 (1735) and GPT-6 Astra (1542).

3. 1 Million Token Context

With a 1M token context window and up to 128k output tokens, Opus can:

Analyze entire books, codebases, or long legal documents in a single prompt.
Hold context across very long agentic sessions.
Use adaptive thinking (always on) to spend more effort on harder problems.

4. Cheaper and Faster

API pricing is $4 / $20 per million tokens, 20% lower than Opus 5. Cache reads drop 60% to $0.20. Because it also uses fewer tokens per task, typical workloads cost about 40% less, and output is more than 30% faster.

5. Clearer Writing, Stronger Safety

Opus 5.5 puts the most important information first, avoids jargon, and follows your style rules. It also posts the strongest results Anthropic has published on its automated behavioral audit, and it's more resistant to prompt injection than earlier models.

Best Use Cases

Coding Agents Large refactors, migrations, and multi-step terminal work.

Research & Analysis Synthesizing trends from multiple complex reports.

Writing Clear, well-structured prose with the key point up front.

Agentic Workflows Planning and executing multi-step tasks over long sessions.

Getting Started

To use Claude Opus, you can:

Subscribe to Claude Pro, Max, Team or Enterprise on claude.ai. Opus isn't included on the free plan.
Use the Claude Platform API, Amazon Bedrock, Google Cloud Vertex AI, or Microsoft Foundry with model ID claude-opus-5-5 (for developers).

"On our agentic coding tasks, Claude Opus 5.5 matched Opus 5's quality in about half the turns, time and output tokens, cutting the cost of that workload by 40 to 50%." — Optiver