Choose Claude Opus 5 (Fast) if…
No advantage on the data we track — pick it for provider preference or output quality on your own prompts.
Claude Opus 5 (Fast) vs OpenAI: GPT-6 Astra Pro
OpenAI: GPT-6 Astra Pro comes out ahead on the data we track: 1 advantage and none for Claude Opus 5 (Fast).
Key numbers
| Spec | Claude Opus 5 (Fast) | OpenAI: GPT-6 Astra Pro |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Input price (per 1M tokens) | $10.00 | $10.00 |
| Output price (per 1M tokens) | $50.00 | $50.00 |
| Blended price (3:1 input/output) | $20.00 | $20.00 |
| Cheaper than … of all models we track | 3% | 3% |
| Context window | 1M tokens (~1,500 pages) | 1.1M tokens (~1,575 pages) |
| Larger context than … of all models | 69% | 93% |
| Max output per response | 128K tokens (~96,000 words) | 128K tokens (~96,000 words) |
| Input types | text, image, file | file, image, text |
| Output types | text | text |
| Free variant | No | No |
| Listed since | 2026-07-24 | 2026-09-04 |
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What it costs for real workloads
Monthly cost at list price for five common workloads. Token counts per unit are stated so you can scale them to your own traffic. A workload that does not fit a model's context window is marked rather than priced.
| Workload (per month) | Claude Opus 5 (Fast) | OpenAI: GPT-6 Astra Pro | Difference |
|---|---|---|---|
| Customer-support chatbot 50,000 conversations — each a 6-turn conversation (1,500 in / 400 out tokens) | $1,750 | $1,750 | — |
| RAG search over documents 20,000 questions — each a question answered from ~8 retrieved passages (6,000 in / 500 out tokens) | $1,700 | $1,700 | — |
| Coding / tool-using agent 2,000 tasks — each a multi-step task with tool calls and file context (60,000 in / 6,000 out tokens) | $1,800 | $1,800 | — |
| Batch summarisation 10,000 documents — each a 6,000-word report summarised to a page (8,000 in / 600 out tokens) | $1,100 | $1,100 | — |
| Long-document analysis 500 documents — each a 150-page contract or codebase read in one pass (100,000 in / 2,000 out tokens) | $550 | $550 | — |
Capabilities side by side
| Capability | Claude Opus 5 (Fast) | OpenAI: GPT-6 Astra Pro | What it lets you do |
|---|---|---|---|
| Tool / function calling | ✓ Yes | ✓ Yes | call your APIs and run agent loops |
| Structured output (JSON schema) | ✓ Yes | ✓ Yes | return JSON that validates against your schema |
| Reasoning / thinking mode | ✓ Yes | ✓ Yes | spend extra tokens thinking before answering hard problems |
| Image input | ✓ Yes | ✓ Yes | read screenshots, charts and scanned pages |
| Audio input | — | — | take speech or audio directly |
| File / PDF input | ✓ Yes | ✓ Yes | accept documents without your own parsing step |
| Image output | — | — | generate images, not just text |
| Built-in web search | ✓ Yes | ✓ Yes | answer from live web results |
| Seed (reproducible sampling) | — | ✓ Yes | repeat a generation for tests and evals |
| Log-probabilities | — | — | read token confidence for classification and scoring |
From each model's published parameters and input/output types. “—” means not advertised, not proven absent.
Price history
- Claude Opus 5 (Fast): price unchanged since we started tracking it on 2026-08-06.
- OpenAI: GPT-6 Astra Pro: price unchanged since we started tracking it on 2026-09-05.
Which should you choose?
Choose OpenAI: GPT-6 Astra Pro if…
- you need seed (reproducible sampling) — to repeat a generation for tests and evals; Claude Opus 5 (Fast) does not advertise it
Frequently asked questions
Is Claude Opus 5 (Fast) better than OpenAI: GPT-6 Astra Pro?
OpenAI: GPT-6 Astra Pro comes out ahead on the data we track: 1 advantage and none for Claude Opus 5 (Fast).
Which is cheaper, Claude Opus 5 (Fast) or OpenAI: GPT-6 Astra Pro?
They cost the same: $20.00 per 1M tokens at a 3:1 input/output mix.
How much do Claude Opus 5 (Fast) and OpenAI: GPT-6 Astra Pro cost per million tokens?
Claude Opus 5 (Fast) costs $10.00 per 1M input tokens and $50.00 per 1M output tokens; OpenAI: GPT-6 Astra Pro costs $10.00 input and $50.00 output. Output tokens are billed separately, so long answers shift the gap.
Which has the bigger context window, Claude Opus 5 (Fast) or OpenAI: GPT-6 Astra Pro?
OpenAI: GPT-6 Astra Pro: 1.1M tokens, about 1,575 pages, against 1M (about 1,500 pages) for Claude Opus 5 (Fast).
Do Claude Opus 5 (Fast) and OpenAI: GPT-6 Astra Pro support function calling and JSON output?
Tool calling — Claude Opus 5 (Fast): yes, OpenAI: GPT-6 Astra Pro: yes. JSON-schema structured output — Claude Opus 5 (Fast): yes, OpenAI: GPT-6 Astra Pro: yes.
Can Claude Opus 5 (Fast) or OpenAI: GPT-6 Astra Pro read images?
Yes, both accept image input.
Is Claude Opus 5 (Fast) or OpenAI: GPT-6 Astra Pro free to use?
No free variant is listed for either; both are pay-per-token.
What is the maximum output length of Claude Opus 5 (Fast) and OpenAI: GPT-6 Astra Pro?
Claude Opus 5 (Fast) can write up to 128K tokens (about 96,000 words) per response; OpenAI: GPT-6 Astra Pro up to 128K (about 96,000 words).
When were Claude Opus 5 (Fast) and OpenAI: GPT-6 Astra Pro released?
Claude Opus 5 (Fast) was listed on 2026-07-24; OpenAI: GPT-6 Astra Pro on 2026-09-04.
About the two models
Claude Opus 5 (Fast)
Fast-mode variant of [Opus 5](/anthropic/claude-opus-5) - identical capabilities with higher output speed at 2x pricing relative to regular Opus 5. Learn more in Anthropic's docs: https://platform.claude.com/docs/en/build-with-claude/fast-mode
Full Claude Opus 5 (Fast) specs →OpenAI: GPT-6 Astra Pro
GPT-6 Astra Pro is the same underlying model as [GPT-6 Astra](https://openrouter.ai/openai/gpt-6-astra), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. **Cost note:** pro mode spends far more...
Full OpenAI: GPT-6 Astra Pro specs →