Which is cheaper, Claude Opus 5.5 or GPT-6 Astra?
Claude Opus 5.5, at $4 input and $20 output per 1M tokens. GPT-6 Astra is $10 input and $50 output at OpenAI's short-context rates, so Astra costs 2.5x as much on both sides.
Model vs model
Claude Opus 5.5 vs GPT-6 Astra
Claude Opus 5.5 costs $4/$20 and GPT-6 Astra costs $10/$50 per 1M input/output tokens on the API.
· today
Quick answer
Pick Claude Opus 5.5 if you want the flagship model at the lower price, or if you work in Claude Code, where it is already the default: it costs $4 / $20 per 1M tokens against GPT-6 Astra's $10 / $50. Pick GPT-6 Astra if you live in ChatGPT and Codex and want what OpenAI calls its most capable model. Both have roughly 1M-token context windows.
Claude Opus 5.5 vs GPT-6 Astra specs
| Spec | Claude Opus 5.5 | GPT-6 Astra |
|---|---|---|
| Released | Sep 22, 2026 | - |
| Status | Available | Available |
| API model ID | claude-opus-5-5 | gpt-6-astra |
| API price (in / out) | $4 / $20 per 1M tokens | $10 / $50 per 1M tokens |
| Cache read | $0.20 per 1M tokens | $1 per 1M tokens |
| Context window | 1M tokens | 1.05M tokens |
| Plans | Pro, Max, Team, Enterprise | - |
| Platforms | Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud, Microsoft Foundry | OpenAI API |
| Runs in | Claude, Claude Code | ChatGPT, Codex |
"-" means we could not verify the value on a vendor page, not that it doesn't exist.
Claude Opus 5.5 vs GPT-6 Astra FAQ
Which has the bigger context window?
They are close: GPT-6 Astra lists 1.05M tokens and Claude Opus 5.5 lists 1M. Both allow up to 128k output tokens.
Which one do the coding agents use by default?
Claude Code defaults to Opus 5.5 on Pro, Max, Team, Enterprise and the API. Codex defaults to GPT-6 Sol, not Astra; you select Astra yourself.
Are there head-to-head benchmarks?
Not from a neutral source we can cite. Anthropic publishes Opus 5.5 scores on its launch page (for example 66.4% on Terminal-Bench 4.0), but we could not load OpenAI's Astra launch page to compare like for like, so we leave that out.
Also compared
Sources
- Claude Developer Platform release notesread 2026-09-24
- Claude API pricingread 2026-09-24
- Claude models overviewread 2026-09-24
- Claude Code model configurationread 2026-09-24
- Claude plans and pricingread 2026-09-24
- Anthropic: Claude Opus 5.5 launchread 2026-09-24
- OpenAI: ChatGPT and Codex modelsread 2026-09-24
- OpenAI API modelsread 2026-09-24
- OpenAI API: GPT-6 Astraread 2026-09-24
- OpenAI API pricingread 2026-09-24