Claude Fable 5.1 vs GPT-6 Astra
Claude Fable 5.1 and GPT-6 Astra are priced the same, $10 input and $50 output per 1M tokens, and their coding scores are close. Astra leads Terminal-Bench 4.0 by 2.1 points and FrontierCode 1.1 by 3.0; Fable 5.1 leads Humanity's Last Exam with tools by 7.8. Fable's cached input costs a quarter of Astra's.
Two flagships at one price
Anthropic released Fable 5.1 on 1 September 2026, and GPT-6 Astra was first listed on the API three days later, on 4 September. Astra reads up to 1.05M tokens, Fable 5.1 up to 1M, and both write up to 128K.
Uncached, our feature session costs $54 on both and a long agent day $488. The cache splits them: cached input is $0.25 on Fable 5.1 and $1 on Astra, so the cached feature session costs $11.88 against $15.12 and the cached long day $92.63 against $123.
Reading the scores
Terminal-Bench 4.0: Astra 57.9%, Fable 5.1 55.8%. The Astra figure is OpenAI's, at high effort, as Anthropic quoted it. FrontierCode 1.1: Astra 53.3%, Fable 50.3%. Humanity's Last Exam with tools: Fable 65%, Astra 57.2%.
Makers run these at different settings, so we read the two coding gaps as a tie and the Humanity's Last Exam gap as a real lead for Fable. Anthropic's cheaper Opus 5.5 beats both of them on all three; Opus 5.5 against GPT-6 Astra has the numbers.
Side by side
| Claude Fable 5.1 | GPT-6 Astra | |
|---|---|---|
| Maker | Anthropic | OpenAI |
| Released | 1 September 2026[1] | 4 September 2026[2] first API listing |
| Context window | 1M tokens[1] | 1.05M tokens[3] |
| Max output | 128K tokens[1] | 128K tokens[3] |
| Input price | $10 per 1M tokens[1] | $10 per 1M tokens[3] |
| Output price | $50 per 1M tokens[1] | $50 per 1M tokens[3] |
| Cached input | $0.25 per 1M tokens[4] | $1 per 1M tokens[3] |
| Long prompts | One price | One price |
| Price change | None announced | None announced |
| Open weights | No[1] Offered through the Claude API and cloud platforms; no weights are published. | No[5] Listed as an API model, not in OpenAI's open-weight section. |
| Reads | text, image[1] | text, image[3] |
Benchmarks
Scores as the makers published them, each with its source and date. Makers run these at different settings, so read a gap of a few points as a tie.
| Benchmark | Claude Fable 5.1 | GPT-6 Astra |
|---|---|---|
| Terminal-Bench 4.0Agentic coding tasks in a real terminal. | 55.8%[6] | 57.9%[7] As reported by OpenAI (high effort), quoted by Anthropic. |
| FrontierCode 1.1 (Main)Hard software engineering tasks. | 50.3%[7] Quoted in the Opus 5.5 announcement. | 53.3%[7] Quoted by Anthropic. |
| Humanity's Last Exam (with tools)Expert-level questions across many fields, tools allowed. | 65%[6] The Opus 5.5 announcement later quoted 65.6%. | 57.2%[7] Quoted by Anthropic. |
What a coding session costs
Our own estimate from the list prices above, for three sessions we define: a coding agent resends the conversation with every call, so prompts are large and grow. "Cached" assumes 90% of prompt tokens are read from the prompt cache and leaves out cache write fees. A long-prompt price applies when a call's prompt is over its threshold. Work out your own mix with the token cost calculator.
| Session | Claude Fable 5.1 | Claude Fable 5.1 cached | GPT-6 Astra | GPT-6 Astra cached |
|---|---|---|---|---|
| Quick fix10 calls of 25K prompt and 1.5K output tokens | $3.25 | $1.06 | $3.25 | $1.23 |
| Feature session60 calls of 80K prompt and 2K output tokens | $54 | $11.88 | $54 | $15.12 |
| Long agent day300 calls of 150K prompt and 2.5K output tokens | $488 | $92.63 | $488 | $123 |
Value for money and release gap
GPT-6 Astra is dated 3 days later (GPT-6 Astra: first API listing). Price per point divides our feature-session cost by a published score: lower means more score for the money. It is a rough lens, not a ranking.
| Measure | Claude Fable 5.1 | GPT-6 Astra |
|---|---|---|
| Input tokens per $1 | 100K | 100K |
| Filling the whole context window once | $10 | $10.50 |
| Feature session per point of Terminal-Bench 4.0 | $0.97 | $0.93 |
| Feature session per point of FrontierCode 1.1 (Main) | $1.07 | $1.01 |
| Feature session per point of Humanity's Last Exam (with tools) | $0.83 | $0.94 |
Questions
Is GPT-6 Astra better than Claude Fable 5.1?
On coding benchmarks they are close: Astra scored 57.9% on Terminal-Bench 4.0 and 53.3% on FrontierCode 1.1, Fable 5.1 55.8% and 50.3%. Fable 5.1 leads on Humanity's Last Exam with tools, 65% against 57.2%.
Do Fable 5.1 and GPT-6 Astra cost the same?
Per token, yes: $10 per 1M input tokens and $50 per 1M output tokens. Cached input is $0.25 on Fable 5.1 and $1 on GPT-6 Astra.
Which has more context?
GPT-6 Astra reads up to 1.05M tokens, Fable 5.1 up to 1M. Both write up to 128K tokens in one reply.
Most compared
Any other two models: pick them in the lists at the top of the page.
- Claude Fable 5.1 vs Claude Opus 5.5
- Claude Fable 5 vs Claude Fable 5.1
- Claude Opus 5.5 vs GPT-6 Astra
- GPT-6.1 Sol vs GPT-6 Astra
- Claude Opus 5.5 vs Claude Sonnet 5.5
- Claude Opus 5 vs Claude Opus 5.5
- Claude Sonnet 5 vs Claude Sonnet 5.5
- Claude Haiku 5.5 vs Claude Sonnet 5.5
- Claude Haiku 4.5 vs Claude Haiku 5.5
- Claude Opus 5.5 vs GPT-6.1 Sol
- Claude Sonnet 5.5 vs GPT-6.1 Sol
- Claude Opus 5.5 vs GPT-5.6 Sol
- Claude Haiku 5.5 vs GPT-6 Luna
- GPT-6.1 Sol vs GPT-6 Sol
- Claude Opus 5.5 vs Gemini 4 Argon
- Claude Sonnet 5.5 vs Gemini 4 Argon
- Claude Opus 5.5 vs Gemini 3.1 Pro Preview
- Gemini 4 Argon vs GPT-6.1 Sol
- Gemini 3.1 Pro Preview vs Gemini 4 Argon
- Claude Haiku 5.5 vs Gemini 3.8 Flash
- Claude Opus 5.5 vs Grok 4.7
- Claude Opus 5.5 vs DeepSeek V4 Pro
- Claude Sonnet 5.5 vs Kimi K3
- Claude Sonnet 5.5 vs GLM-5.3
More tools
Sources
- platform.claude.com: docs/en/models/fable-5-1/overview, read
- openrouter.ai: openai/gpt-6-astra, read
- developers.openai.com: api/docs/models/gpt-6-astra, read
- platform.claude.com: docs/en/about-claude/pricing, read
- developers.openai.com: api/docs/models/all, read
- anthropic.com: claude-fable-and-mythos-5-1, read
- anthropic.com: claude-opus-5-5, read
Numbers from the makers' own pages, checked by hand, last read . List prices in US dollars before tax. Spotted a mistake? office@shuriken.sh.
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