Claude Fable 5.1
- Input / 1M tokens
- $10.00
- Output / 1M tokens
- $50.00
- Providers
- 4
- Uptime, 24 h
- 100%
API models · Side by side
Claude Fable 5.1 vs GPT-6 Astra
Claude Fable 5.1 and GPT-6 Astra are the premium models from Anthropic and OpenAI, and they list at the same price. If your prompts are short, cost won't decide this. If you send long documents or run agents on a cached context, Fable is much cheaper. If you need answers faster, only Astra sells a faster tier.
GPT-6 Astra
- Input / 1M tokens
- $10.00
- Output / 1M tokens
- $50.00
- Providers
- 3
- Uptime, 24 h
- 100%
The short answer
Both charge $10 per million input tokens and $50 per million output tokens, so short requests cost the same. Astra raises that to $20 and $75 once a prompt passes 272,000 tokens, and its cache reads cost $1 per million against Fable's $0.25. Fable keeps one rate across its whole 1 million token window. Astra offers Fast and Ultrafast tiers; Anthropic rates Fable as slower and sells no fast mode for it.
Estimate your monthly bill
Enter your own usage. We apply each model's current rates, including long-prompt pricing, for a 30-day month.
Try:
Claude Fable 5.1$1,350.00per month
GPT-6 Astra$1,350.00per month
A token is roughly three-quarters of an English word. Cached input, reasoning tokens, tools and media are not included.
Compare the details
Compare context, supported inputs and usage costs. Highlighted rows show a difference.
| Feature | Claude Fable 5.1 | GPT-6 Astra |
|---|---|---|
| Input formats | file, image, text | file, image, text |
| Output formats | text | text |
| Context / position limit | 1,000,000 | 1,050,000 |
| Endpoint output limit (tokens) | 128,000 | 128,000 |
| Developer features | Reasoning output, Completion limit, Output limit, Reasoning controls, Thinking effort, Response format, Stop sequences, Structured output, Tool selection, Tool calling, Response length | Reasoning output, Completion limit, Output limit, Reasoning controls, Thinking effort, Response format, Seed, Structured output, Tool selection, Tool calling, Response length |
| Cached input / 1M tokens | $0.25 | $1.00 |
| Cache write / 1M tokens | $12.50 | $12.50 |
| USD input / 1M tokens | $10.00 | $10.00 |
| USD output / 1M tokens | $50.00 | $50.00 |
| Available API providers | 4 | 3 |
| Best provider uptime, last 24 h | 100% | 100% |
| Model identifier | anthropic/claude-fable-5.1 | openai/gpt-6-astra |
API pricing
Prices are in USD per million tokens. Input is what you send; output is what the model generates. Chat subscriptions and API usage are billed separately.
GPT-6 Astra: long-prompt rates
- Long-prompt threshold: 272,000 prompt tokens. Input: $20.00 / 1M. Output: $75.00 / 1M.
Tools, images and additional reasoning can add charges. The examples below cover input and output tokens only.
Compare local modelsWhat those prices mean in practice
Each example uses the same token budget for both models. These are calculations, not measured workloads. Cache discounts, media, tools and extra reasoning are excluded.
| Workload | Claude Fable 5.1 | GPT-6 Astra |
|---|---|---|
| 1,000 short requestsPer request: 2,000 input + 500 output tokens | $45.00 | $45.00 |
| 100 document summariesPer request: 20,000 input + 1,000 output tokens | $25.00 | $25.00 |
| 10 long-document requestsPer request: 300,000 input + 2,000 output tokens | $31.00 | $61.50 |
Estimate = requests × (input tokens × input price + output tokens × output price) ÷ 1,000,000. Long-prompt rates are applied where the pricing data provides them. Real requests can use different amounts of output.
Beyond the price tag
Short requests cost the same
At 1,000 short requests a day (2,000 tokens in, 500 out), both models come to about $1,350 a month. Batch processing halves both, to $5 and $25 per million. Actual bills can still differ, because both models bill their reasoning as output and may think and write different amounts for the same task. Compare real runs, not just the price list.
Long prompts cost about twice as much on Astra
Past 272,000 input tokens, Astra charges $20 in and $75 out for the entire request, not just the extra tokens. Fable charges its normal rates across the full window. Ten 300,000-token requests with 2,000-token replies cost $31 on Fable and $61.50 on Astra. Astra's 1.05 million token window looks bigger, but OpenAI caps input at 922,000 tokens, so capacity is unlikely to decide this for you.
Caching is where agents save the most
An agent re-sends its context at every step, so most of its input should be cache reads. Take a run that caches a 200,000-token context once, re-reads it on 50 steps and writes 2,000 tokens each time: about $10 on Fable and $17.50 on Astra. With a 300,000-token context, Astra's long-prompt rates apply and the gap widens to about $12.50 against $45. These figures ignore the small uncached part of each prompt, and reasoning would add to both.
How long the cache lasts
The first cache write costs $12.50 per million on both, but the terms differ. Astra caches automatically and holds a prefix for at least 30 minutes; 12 hours costs $25 per million. On Fable you opt in, and the $12.50 write lasts 5 minutes, renewed free each time the cache is read. An hour costs $20. If your agent can pause for more than 5 minutes between steps, such as while waiting for a person, budget for the hour-long Fable write or expect to pay for fresh writes.
Speed
Anthropic lists Fable 5.1 as slower than the rest of its lineup, and its fast mode covers Opus models, not Fable. Astra has Fast at double the rates ($20 and $100 per million) and Ultrafast at six times ($60 and $300), and both rise further on long prompts. OpenAI gives no latency guarantee for Fast. Fast isn't available with EU data residency, and Ultrafast only runs with US residency or global processing.
Differences to plan for in your code
Reasoning stays on for both, and neither accepts temperature or top_p. Beyond that, Fable returns an error if you force a tool call or prefill a reply. Its safety classifiers can also decline a request, which comes back as a normal response with a refusal stop reason, and some refusals are billed. Build a retry for that; Anthropic allows Opus 4.8 and Opus 5 as fallback models. On Astra, tool calling requires the Responses API even though Chat Completions is supported.
Data handling and where each one runs
Fable carries 30-day data retention, and zero data retention needs Anthropic's express authorization. OpenAI's data page lists no Astra-specific exception: zero data retention on the Responses API needs OpenAI's prior approval and comes with limitations. Fable is available on the Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry. For data location, Astra offers regional processing in the US and Europe, and Fable's option on the Claude API is US-only. Both add 10% to token prices.
Which one should you pick?
Choose Fable 5.1 for long documents and agents that re-read a large context, since it costs less for the same list price. Choose GPT-6 Astra if response time matters enough to pay for Fast, or if you already build on the Responses API and its hosted tools. Before either, try the cheaper sibling: Anthropic suggests starting most work on Opus 5.5 ($4 and $20), and OpenAI describes GPT-6.1 Sol ($2 and $10) as near-Astra performance for less.
Common questions
Is Claude Fable 5.1 better than GPT-6 Astra?
We don't name an overall winner, because that depends on your tasks. Anthropic aims Fable at demanding reasoning and long-running agent work, and OpenAI aims Astra at its most demanding reasoning, coding and professional work. Test both on real examples at comparable effort settings.
Do they really cost the same?
Only at list rates on prompts up to 272,000 tokens without caching. Above that, Astra costs more. Cache reads also favour Fable at every prompt size, $0.25 against $1 per million.
Can I switch between them without changing my code?
Not cleanly. Each vendor's API has its own rules for tool calls, reasoning settings and caching. Budget time to retest your prompts as well.
Are these ChatGPT or Claude subscription prices?
No. They're pay-per-use API prices for building apps. The Claude and ChatGPT apps have their own monthly plans.