# Claude Opus 5.5 vs GPT-6 Astra

URL: https://aistack.sh/compare/claude-opus-5-5-vs-gpt-6-astra
Last updated: 2026-09-24
Model pages: https://aistack.sh/model/claude-opus-5-5, https://aistack.sh/model/gpt-6-astra

## 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.

## 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 the value could not be verified on a vendor page.

## FAQ

### 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.

### 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

- [Claude Fable 5.1 vs Claude Opus 5.5](https://aistack.sh/compare/claude-fable-5-1-vs-claude-opus-5-5)
- [Claude Opus 5.5 vs GPT-6 Sol](https://aistack.sh/compare/claude-opus-5-5-vs-gpt-6-sol)
- [GPT-6 Astra vs GPT-6 Sol](https://aistack.sh/compare/gpt-6-astra-vs-gpt-6-sol)

## Sources

- [Claude Developer Platform release notes](https://platform.claude.com/docs/en/release-notes/overview), read 2026-09-24
- [Claude API pricing](https://platform.claude.com/docs/en/about-claude/pricing), read 2026-09-24
- [Claude models overview](https://platform.claude.com/docs/en/about-claude/models/overview), read 2026-09-24
- [Claude Code model configuration](https://code.claude.com/docs/en/model-config), read 2026-09-24
- [Claude plans and pricing](https://claude.com/pricing), read 2026-09-24
- [Anthropic: Claude Opus 5.5 launch](https://www.anthropic.com/claude-opus-5-5), read 2026-09-24
- [OpenAI: ChatGPT and Codex models](https://learn.chatgpt.com/docs/models), read 2026-09-24
- [OpenAI API models](https://developers.openai.com/api/docs/models), read 2026-09-24
- [OpenAI API: GPT-6 Astra](https://developers.openai.com/api/docs/models/gpt-6-astra), read 2026-09-24
- [OpenAI API pricing](https://developers.openai.com/api/docs/pricing), read 2026-09-24