Choose Anthropic: Claude Fable 5.1 if…
No advantage on the data we track — pick it for provider preference or output quality on your own prompts.
Anthropic: Claude Fable 5.1 vs OpenAI: GPT-6 Astra Pro
OpenAI: GPT-6 Astra Pro comes out ahead on the data we track: 1 advantage and none for Anthropic: Claude Fable 5.1.
Key numbers
| Spec | Anthropic: Claude Fable 5.1 | 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 | 2026-09-01 | 2026-09-04 |
Advertisement
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) | Anthropic: Claude Fable 5.1 | 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 | Anthropic: Claude Fable 5.1 | 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
- Anthropic: Claude Fable 5.1: price unchanged since we started tracking it on 2026-09-02.
- 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; Anthropic: Claude Fable 5.1 does not advertise it
Frequently asked questions
Is Anthropic: Claude Fable 5.1 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 Anthropic: Claude Fable 5.1.
Which is cheaper, Anthropic: Claude Fable 5.1 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 Anthropic: Claude Fable 5.1 and OpenAI: GPT-6 Astra Pro cost per million tokens?
Anthropic: Claude Fable 5.1 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, Anthropic: Claude Fable 5.1 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 Anthropic: Claude Fable 5.1.
Do Anthropic: Claude Fable 5.1 and OpenAI: GPT-6 Astra Pro support function calling and JSON output?
Tool calling — Anthropic: Claude Fable 5.1: yes, OpenAI: GPT-6 Astra Pro: yes. JSON-schema structured output — Anthropic: Claude Fable 5.1: yes, OpenAI: GPT-6 Astra Pro: yes.
Can Anthropic: Claude Fable 5.1 or OpenAI: GPT-6 Astra Pro read images?
Yes, both accept image input.
Is Anthropic: Claude Fable 5.1 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 Anthropic: Claude Fable 5.1 and OpenAI: GPT-6 Astra Pro?
Anthropic: Claude Fable 5.1 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 Anthropic: Claude Fable 5.1 and OpenAI: GPT-6 Astra Pro released?
Anthropic: Claude Fable 5.1 was listed on 2026-09-01; OpenAI: GPT-6 Astra Pro on 2026-09-04.
About the two models
Anthropic: Claude Fable 5.1
Claude Fable 5.1 improves on Claude Fable 5 across the board, with the biggest gains in agentic coding, long-running agentic workflows, and knowledge work: long code refactors, front-end and visual...
Full Anthropic: Claude Fable 5.1 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 →