Claude Fable 5.1 vs Fugu Ultra vs Claude Mythos 5
Too close to call on our weighted score (Claude Fable 5.1 36, Claude Mythos 5 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
- Anthropic
Claude Mythos 5
36/100- ECI—
- Price$10.00 / $50.00
- Context1M
Too close to call
It is close. Our weighted score puts them within a point (Claude Fable 5.1 36/100, Claude Mythos 5 36/100, Fugu Ultra 33/100), so choose by what matters most for your work: Fugu Ultra on price. 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 · Claude Mythos 5 $20.00 per 1M tokens (3:1 blend)
- Longest contextAbout the sameClaude Fable 5.1 1,000,000 · Fugu Ultra 1,000,000 · Claude Mythos 5 1,000,000 tokens
- Widest inputsClaude Fable 5.1 and Claude Mythos 5Claude Fable 5.1: Text, Images, PDFs · Fugu Ultra: Text, Images · Claude Mythos 5: Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Claude Fable 5.1 | Fugu Ultra | Claude Mythos 5 |
|---|---|---|---|---|
| Price | 50% | 0 | 0 | 0 |
| Inputs & features | 30% | 80 | 70 | 80 |
| Context window | 20% | 60 | 60 | 60 |
| 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 | Claude Mythos 5Anthropic |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 164.8 | — | — |
| ECI rank | #4 of 148 | — | — |
| FrontierMath Tiers 1–3Research-level mathematics | 90.2% | — | — |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% | — | — |
| SimpleQA VerifiedShort factual questions | 70.8% | — | — |
| 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 | — |
| Blended (3:1) | $20.00 | $11.25 (best) | $20.00 |
| Long-context rate | Same rate | Over 272K: $10.00 / $45.00 | Same rate |
| Price source | Official Anthropic API | Official Sakana AI API | Median of 2 providers |
| Limits | |||
| Context window | 1,000,000 tokens | 1,000,000 tokens | 1,000,000 tokens |
| 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 | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | claude-fable-5-1 | fugu-ultra | — |
| API providers | 29 (best) | 11 | 2 |
| Released | Sep 1, 2026 | Jun 15, 2026 | Jun 9, 2026 |
| Knowledge cutoff | Jun 2026 | — | Jan 31, 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
- Claude Mythos 5$200.00
Which should you choose?
Which is better: Claude Fable 5.1, Fugu Ultra or Claude Mythos 5?
It is close. Our weighted score puts them within a point (Claude Fable 5.1 36/100, Claude Mythos 5 36/100, Fugu Ultra 33/100), so choose by what matters most for your work: Fugu Ultra on price. 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 Claude Mythos 5?
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); Claude Mythos 5 costs $10.00 input / $50.00 output per million tokens (median across 2 API providers). 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 Claude Mythos 5 (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 Claude Mythos 5 has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Fable 5.1, Fugu Ultra and Claude Mythos 5 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?
Claude Fable 5.1, Fugu Ultra and Claude Mythos 5 share the same 1,000,000-token context window. Maximum output per response: Claude Fable 5.1 up to 128,000, Claude Mythos 5 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; Claude Mythos 5 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 Claude Mythos 5 are proprietary and only available through APIs and apps.
Which is newer?
Claude Fable 5.1 is the newest, released Sep 1, 2026. Fugu Ultra came out Jun 15, 2026; Claude Mythos 5 came out Jun 9, 2026. Knowledge cutoff: Claude Fable 5.1 Jun 2026, Claude Mythos 5 Jan 31, 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.
