Claude Opus 5.5 vs GPT-6 Astra
How Anthropic's Claude Opus 5.5 compares to OpenAI's GPT-6 Astra on agentic coding, knowledge work, reasoning, and price.
The Verdict
"Opus 5.5 wins agentic coding and knowledge work at 2.5× lower cost; Astra leads on science and some business-workflow tasks."
Two new flagships landed three weeks apart in September 2026: OpenAI's GPT-6 Astra (September 3) and Anthropic's Claude Opus 5.5 (September 22). On paper they look similar: both have context windows of about 1M tokens and both cap output at 128k tokens. In practice they differ a lot on price and on what they're best at.
At a Glance
| Feature | Claude Opus 5.5 | GPT-6 Astra |
|---|---|---|
| Primary Strength | Agentic Coding & Knowledge Work | Scientific Research & Frontier Reasoning |
| Context Window | 1M tokens | 1.05M tokens |
| Max Output | 128k tokens | 128k tokens |
| Terminal-Bench 4.0 | 66.4% | 57.9% |
| FrontierCode v1.1 | 54.4% | 53.3% |
| GDPval-AA v2.1 (knowledge work) | 1846 | 1542 |
| Humanity's Last Exam (with tools) | 67.7% | 57.2% |
| Terminal-Bench-Science 0.1 | 58.7% | 64.6% |
| AutomationBench | 40.0% | 41.4% |
| API Pricing (input / output per M) | $4 / $20 | $10 / $50 |
Benchmark figures are from Anthropic's launch announcement (September 22, 2026); Astra scores are as reported by OpenAI.
Where Opus 5.5 Wins
1. Agentic Coding
On Terminal-Bench 4.0, which measures complex, multi-step work in a command line, Opus 5.5 scores 66.4% against Astra's 57.9%. Anthropic reports it matches Astra's Terminal-Bench result at its default effort level for about 40% of the cost.
"In our testing across GitHub Copilot CLI and VS Code, Claude Opus 5.5 used among the fewest tokens and steps we measured." — GitHub
2. Knowledge Work
On GDPval-AA v2.1, a test of real-world professional tasks across many occupations, Opus 5.5 leads by roughly 300 Elo points (1846 vs 1542).
3. Price
Opus 5.5 costs $4 / $20 per million tokens, while Astra costs $10 / $50. That's 2.5× cheaper on both input and output. Cache reads, which dominate the bill for long agent sessions, cost $0.20 vs $1.00. For high-volume agent workloads this is often the deciding factor.
"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
4. Clearer Communication
Anthropic tuned Opus 5.5 to put the most important information first and avoid jargon, which makes long working sessions easier to follow and check.
When to Choose GPT-6 Astra
Astra is a strong model and leads in a few areas:
- Scientific research: It scores higher on Terminal-Bench-Science (64.6% vs 58.7%).
- Business workflow automation: It edges ahead on AutomationBench (41.4% vs 40.0%).
- Frontend UI generation: Independent leaderboards rank it highly for producing working UI code.
- Existing OpenAI stack: If your tooling is built around ChatGPT or the OpenAI API, switching costs matter.
Verdict
For agentic coding, long-running agents, and professional knowledge work, Claude Opus 5.5 is the stronger choice, and it's 2.5× cheaper.
For frontier scientific research or a team already committed to the OpenAI ecosystem, GPT-6 Astra is worth testing on your own workload.