Claude Fable 5.1 vs Fugu Ultra vs GPT-6 Astra
Too close to call on our weighted score (GPT-6 Astra 36, Claude Fable 5.1 36, Fugu Ultra 33). The right pick depends on what you value most.
AnthropicClaude Fable 5.1
36/100- ECI164.8
- Price$10.00 / $50.00
- Context1M
Sakana AI
Fugu Ultra
33/100- ECI—
- Price$5.00 / $30.00
- Context1M
OpenAIGPT-6 Astra
36/100- ECI166.5
- Price$10.00 / $50.00
- Context1.05M
Too close to call
It is close. Our weighted score puts them within a point (GPT-6 Astra 36/100, Claude Fable 5.1 36/100, Fugu Ultra 33/100), so choose by what matters most for your work: Fugu Ultra on price and GPT-6 Astra for long inputs. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
- CapabilityNot enough dataNo independent benchmark covers every model here yet
- Lowest priceFugu UltraFugu Ultra $11.25 · Claude Fable 5.1 $20.00 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 AstraGPT-6 Astra 1,050,000 · Claude Fable 5.1 1,000,000 · Fugu Ultra 1,000,000 tokens
- Widest inputsClaude Fable 5.1 and GPT-6 AstraClaude Fable 5.1: Text, Images, PDFs · Fugu Ultra: Text, Images · GPT-6 Astra: Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Claude Fable 5.1 | Fugu Ultra | GPT-6 Astra |
|---|---|---|---|---|
| Price | 50% | 0 | 0 | 0 |
| Inputs & features | 30% | 80 | 70 | 80 |
| Context window | 20% | 60 | 60 | 61 |
| Overall | 100% | 36/100 | 33/100 | 36/100 |
Left out because at least one model lacks the data: capability. The remaining weights were rescaled.
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Fable 5.1Anthropic | Fugu UltraSakana AI | GPT-6 AstraOpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 164.8 | — | 166.5 (best) |
| ECI rank | #4 of 148 | — | #2 of 148 (best) |
| GPQA DiamondGraduate-level science questions | — | — | 95.8% |
| FrontierMath Tiers 1–3Research-level mathematics | 90.2% | — | 93.7% (best) |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% | — | 100% |
| SimpleQA VerifiedShort factual questions | 70.8% | — | 75.6% (best) |
| Price per million tokens | |||
| Input | $10.00 | $5.00 (best) | $10.00 |
| Output | $50.00 | $30.00 (best) | $50.00 |
| Cached input | $0.25 (best) | $0.50 | $1.00 |
| Blended (3:1) | $20.00 | $11.25 (best) | $20.00 |
| Long-context rate | Same rate | Over 272K: $10.00 / $45.00 | Over 272K: $20.00 / $75.00 |
| Price source | Official Anthropic API | Official Sakana AI API | Official OpenAI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,000,000 tokens | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | — | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | No | Yes |
| Audio | No | No | No |
| Video | No | No | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeshigh · xhigh | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | claude-fable-5-1 | fugu-ultra | gpt-6-astra |
| API providers | 29 (best) | 11 | 26 |
| Released | Sep 1, 2026 | Jun 15, 2026 | Sep 4, 2026 |
| Knowledge cutoff | Jun 2026 | — | Apr 30, 2026 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Claude Fable 5.1$200.00
- Fugu Ultra$110.00
- GPT-6 Astra$200.00
Which should you choose?
Which is better: Claude Fable 5.1, Fugu Ultra or GPT-6 Astra?
It is close. Our weighted score puts them within a point (GPT-6 Astra 36/100, Claude Fable 5.1 36/100, Fugu Ultra 33/100), so choose by what matters most for your work: Fugu Ultra on price and GPT-6 Astra for long inputs. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
Which is cheaper, Claude Fable 5.1, Fugu Ultra or GPT-6 Astra?
Fugu Ultra is cheaper at $5.00 input / $30.00 output per million tokens (official Sakana AI API price). Claude Fable 5.1 costs $10.00 input / $50.00 output per million tokens (official Anthropic API price); GPT-6 Astra costs $10.00 input / $50.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $11.25 per million tokens for Fugu Ultra versus $20.00 for Claude Fable 5.1 (1.8× as much) and $20.00 for GPT-6 Astra (1.8× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers all three models yet. Claude Fable 5.1 has an ECI of 164.8, Fugu Ultra has not been scored yet and GPT-6 Astra has an ECI of 166.5.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Fable 5.1, Fugu Ultra and GPT-6 Astra yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. All three support tool calling for agent workflows.
Which has the bigger context window?
GPT-6 Astra has the largest context window at 1,050,000 tokens, against 1,000,000 for Claude Fable 5.1 and 1,000,000 for Fugu Ultra. Maximum output per response: Claude Fable 5.1 up to 128,000, GPT-6 Astra up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Fable 5.1 accepts text, images and PDFs; Fugu Ultra accepts text and images; GPT-6 Astra accepts text, images and PDFs. Claude Fable 5.1 handles the widest range of inputs.
Are any of these open source?
No. Claude Fable 5.1, Fugu Ultra and GPT-6 Astra are proprietary and only available through APIs and apps.
Which is newer?
GPT-6 Astra is the newest, released Sep 4, 2026. Claude Fable 5.1 came out Sep 1, 2026; Fugu Ultra came out Jun 15, 2026. Knowledge cutoff: Claude Fable 5.1 Jun 2026, GPT-6 Astra Apr 30, 2026.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
