Claude Fable 5 vs Fugu Ultra v2.0
Anthropic · US | Sakana AI · Global · Updated June 2026
Quick verdict
Pick Claude Fable 5 for the hardest reasoning and most complex problems or long-horizon, multi-step agentic work. Pick Fugu Ultra v2.0 for sakana's own evaluation reports best-or-joint-best results on 5 of 8 benchmarks tested, including a 74.3 on the deepswe coding-repair benchmark or claims to outperform flagship models like gpt-6 astra and claude fable 5.1 despite its underlying orchestration pool reportedly excluding both of them. On a tight budget at scale, Fugu Ultra v2.0 is the value pick.
Claude Fable 5 (Anthropic) and Fugu Ultra v2.0 (Sakana AI) are two of the models people most often weigh against each other in 2026. Claude Fable 5 is anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive. Fugu Ultra v2.0 is sakana AI's flagship multi-agent orchestration model, claiming best-or-joint-best results on 5 of 8 self-reported benchmarks against monolithic frontier models — $5/$30 per million tokens. Their biggest split is price, and the breakdown below shows exactly how that plays out for your workload.
Key differences at a glance
- ▸Price: Fugu Ultra v2.0 is about 2× cheaper on input ($5/$30 per 1M tokens vs $10/$50 per 1M tokens) — meaningful once you are processing millions of tokens a month.
- ▸Context window: both advertise 1M (~1,500 pages). Tie on paper — test on your own long inputs, since usable recall varies by model.
- ▸Recency: Fugu Ultra v2.0 is the newer model by about 3 months (released September 10, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
| Spec | Claude Fable 5 | Fugu Ultra v2.0 |
|---|---|---|
| Provider | Anthropic (US) | Sakana AI (Global) |
| Released | June 9, 2026 | September 10, 2026 |
| Context window | 1M (~1,500 pages) | 1M tokens (~1,500 pages) |
| Price (in/out) | $10/$50 per 1M tokens | $5/$30 per 1M tokens |
| Open weight? | No — API only | No — API only |
| Modalities | text, image, code | text |
| SWE-Bench Verified | Not published | Not published |
| MRCR v2 @ 1M | Not published | Not published |
Who wins what
The hardest reasoning and most complex problems
Claude Fable 5
Claude Fable 5 lists the hardest reasoning and most complex problems among its strengths; Fugu Ultra v2.0 does not.
Long-horizon, multi-step agentic work
Claude Fable 5
Fugu Ultra v2.0 is comparatively weak here — not a single trained model — Sakana describes Fugu as "a Multi-Agent System, Delivered as One Model" that dynamically routes tasks across a pool of other models, so head-to-head benchmark framing against monolithic frontier models should be read skeptically
Frontier-level analysis and research
Claude Fable 5
Claude Fable 5 lists frontier-level analysis and research among its strengths; Fugu Ultra v2.0 does not.
Sakana's own evaluation reports best-or-joint-best results on 5 of 8 benchmarks tested, including a 74.3 on the DeepSWE coding-repair benchmark
Fugu Ultra v2.0
Sakana AI's flagship multi-agent orchestration model, claiming best-or-joint-best results on 5 of 8 self-reported benchmarks against monolithic frontier models — $5/$30 per million tokens — and it runs cheaper at $5/$30 per 1M tokens.
Claims to outperform flagship models like GPT-6 Astra and Claude Fable 5.1 despite its underlying orchestration pool reportedly excluding both of them
Fugu Ultra v2.0
Claude Fable 5 is comparatively weak here — highest price in the Claude lineup
1M-token context window
Fugu Ultra v2.0
Sakana AI's flagship multi-agent orchestration model, claiming best-or-joint-best results on 5 of 8 self-reported benchmarks against monolithic frontier models — $5/$30 per million tokens — and it is the newer of the two.
Lowest cost at scale
Fugu Ultra v2.0
At $5/$30 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Which should you pick?
A cost-sensitive startup shipping high volume
→ Fugu Ultra v2.0
At $5/$30 per 1M tokens it undercuts Claude Fable 5, and on millions of tokens that margin decides the monthly bill.
Anyone whose priority is the hardest reasoning and most complex problems
→ Claude Fable 5
It is specifically built for that.
Anyone whose priority is sakana's own evaluation reports best-or-joint-best results on 5 of 8 benchmarks tested, including a 74.3 on the deepswe coding-repair benchmark
→ Fugu Ultra v2.0
That is its strongest area.
Claude Fable 5: where it fits
Anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive. Released June 9, 2026 by Anthropic, it is built for the hardest reasoning and most complex problems, long-horizon, multi-step agentic work, frontier-level analysis and research, and work where maximum capability outweighs cost.
Its trade-offs are real: highest price in the Claude lineup, and tier access was temporarily suspended in June 2026 under a US export-control directive. At $10 in / $50 out per million tokens, it sits in the premium price band.
Fugu Ultra v2.0: where it fits
Sakana AI's flagship multi-agent orchestration model, claiming best-or-joint-best results on 5 of 8 self-reported benchmarks against monolithic frontier models — $5/$30 per million tokens. Released September 10, 2026 by Sakana AI, it is built for sakana's own evaluation reports best-or-joint-best results on 5 of 8 benchmarks tested, including a 74.3 on the DeepSWE coding-repair benchmark, claims to outperform flagship models like GPT-6 Astra and Claude Fable 5.1 despite its underlying orchestration pool reportedly excluding both of them, and 1M-token context window.
Its trade-offs: not a single trained model — Sakana describes Fugu as "a Multi-Agent System, Delivered as One Model" that dynamically routes tasks across a pool of other models, so head-to-head benchmark framing against monolithic frontier models should be read skeptically, pricing rises to roughly $10/$45 per million tokens for prompts above 272K tokens, and benchmark comparisons against GPT-6 Astra and Claude Fable 5.1 are Sakana's own self-reported figures, not independently verified head-to-head scores. At $5 in / $30 out per million tokens, it sits in the premium price band.
The bottom line for this matchup
Claude Fable 5 and Fugu Ultra v2.0 overlap enough that the right pick depends on your specific job. Fugu Ultra v2.0 costs less per token; and each leads in its own area — Claude Fable 5 for the hardest reasoning and most complex problems, Fugu Ultra v2.0 for sakana's own evaluation reports best-or-joint-best results on 5 of 8 benchmarks tested, including a 74.3 on the deepswe coding-repair benchmark. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both Claude Fable 5 and Fugu Ultra v2.0 without two subscriptions? LumiChats gives you these plus 40+ models under one ₹69/day pass (about $1/day) — draft with one, cross-check with the other.
See pricingFrequently asked questions
Is Claude Fable 5 or Fugu Ultra v2.0 better for coding?
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, Claude Fable 5 leans toward the hardest reasoning and most complex problems while Fugu Ultra v2.0 leans toward sakana's own evaluation reports best-or-joint-best results on 5 of 8 benchmarks tested, including a 74.3 on the deepswe coding-repair benchmark, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Fable 5 or Fugu Ultra v2.0?
Fugu Ultra v2.0 is cheaper — $10/$50 per 1M tokens vs $5/$30 per 1M tokens, roughly 2× apart on input.
Which has the bigger context window?
Both advertise 1M (~1,500 pages). Remember advertised ≠ usable: recall typically degrades before the ceiling.
Can I use both Claude Fable 5 and Fugu Ultra v2.0 together?
Yes — a multi-model platform like LumiChats gives you Claude Fable 5, Fugu Ultra v2.0 and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, Claude Fable 5 or Fugu Ultra v2.0?
Fugu Ultra v2.0 — released September 10, 2026, about 3 months after Claude Fable 5.
Related comparisons
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.