Claude Fable 5 vs Fugu Ultra 1.1

What I tested — same prompt, two models

I run the same fixed prompt set through every new model the day it drops — same string, one shot, single HTML file out — and I score the result 0–10 on whether it ran, how close it hit the brief, and how good it looked. Below is what came out when I gave the exact same prompts to Claude Fable 5 and Fugu Ultra 1.1, side by side, on 24 shared tasks inside the Agent Operating System.

Both models were given identical prompts inside the Agent Operating System — no help, no iteration, no "best of N" tricks. I run each prompt once, save the HTML file the model produces, and score it 0–10 on whether it ran, how close it hit the brief, and how good it looked. The scoring is mine. The verdicts below are pulled from my source comparison guides at agentos.guide where I publish every score and the reasoning behind it.

Claude Fable 5 · Selected from Agent OS for the highest-stakes work — it replaced Opus 4.8 as the safety net on hard prompts. Its four core 3D games were rebuilt to showcase quality with the threejs-game-director skill, lifting the full 42-task bench to 8.14 avg — the #1 solo model, behind only the Fusion and MoA ensembles.

Fugu Ultra 1.1 · Benched on GoldieBench via Sakana's Responses API (fugu-ultra-v1.1, xhigh reasoning). Game tasks use the skill-infused threejs-game-director prompt plus a controls+graphics fix loop with an anti-regression clamp, judged on a real mid-play frame by the same Opus judge as the field.

Where Claude Fable 5 beat Fugu Ultra 1.1

The tasks where I gave Claude Fable 5 a higher 0–10 score on the same prompt — with the actual commentary from my source guides.

Where Fugu Ultra 1.1 beat Claude Fable 5

The tasks where I gave Fugu Ultra 1.1 a higher 0–10 score on the same prompt — with the actual commentary from my source guides.

Strengths & weaknesses I logged

Pricing & context — the spec sheet

The verdict — which should you pick?

Across 23 scored shared tasks, Claude Fable 5 averaged 8.14/10, beating Fugu Ultra 1.1's 6.94/10 by 1.20 points. Pick Claude Fable 5 when the build has to ship on the first prompt and you can afford the trade-offs in the comparison below.

If you only run one of these inside your stack, the head-to-head average above is the call. If you can run both, my honest play is to wire Claude Fable 5 and Fugu Ultra 1.1 both into the Agent Operating System and dispatch each from the kanban by task type — mission-critical one-shot builds where you want anthropic's newest reasoning → Claude Fable 5, hard, high-stakes coding and reasoning where answer quality beats latency → Fugu Ultra 1.1. That's the same setup I run for the 4,000+ founders inside the AI Profit Boardroom.

FAQ — Claude Fable 5 vs Fugu Ultra 1.1

Which is better, Claude Fable 5 or Fugu Ultra 1.1?

On Goldie Bench, Claude Fable 5 averages 8.14/10 across the shared tasks, with 4 gold, 2 silver, 1 bronze overall. Fugu Ultra 1.1 averages 6.94/10, with 0 gold, 1 silver, 2 bronze. Claude Fable 5 wins the head-to-head 16–5.

How much does Claude Fable 5 cost vs Fugu Ultra 1.1?

Claude Fable 5: Released alongside Mythos 5 on June 9, 2026 as the publicly-available member of the new Mythos class. Premium per-token pricing on the Anthropic API; available everywhere Opus 4.8 ships. Fugu Ultra 1.1: Sakana's Fugu Ultra v1.1 — a multi-agent system served as a model: an orchestrator routes each request across one to three expert agents and synthesises the answer. Reported (v1.0): SWE-Bench Pro 73.7, LiveCodeBench 93.2, GPQA Diamond 95.5. NOTE: Sakana geo-blocks the EU/EEA/UK/Switzerland pending GDPR compliance — benched from an allowed region.

What's the context window for Claude Fable 5 vs Fugu Ultra 1.1?

Claude Fable 5 has a 200,000 tokens (1M with extended thinking) context window. Fugu Ultra 1.1 has a 1,000,000-token context window context window.

When should I pick Claude Fable 5 over Fugu Ultra 1.1?

Pick Claude Fable 5 for: Mission-critical one-shot builds where you want Anthropic's newest reasoning; Long-context work using extended thinking up to 1M tokens; Plan-heavy multi-step tasks where intelligence in the plan matters more than the build. The trade-off is the weaknesses we logged on the bench: Its hardest one-shots (crypt, twilightvale) black-screened on three.js r128 API drift — the scored builds are agentic rebuilds, not the raw first pass, and crypt's AAA rebuild needed a one-line emissive patch; The showcase ceiling shown here needs the threejs-game-director scaffolding baked into the prompt — a bare one-shot lands lower (7.72 avg); Premium $10/$50 per-M pricing — you're paying for reasoning depth; cheaper models stay competitive on pure one-shot visuals.

When should I pick Fugu Ultra 1.1 over Claude Fable 5?

Pick Fugu Ultra 1.1 for: Hard, high-stakes coding and reasoning where answer quality beats latency; Agentic workflows in Codex / Claude Code via the drop-in provider config; One-shot builds you want a panel of experts on, not a single model. The trade-off is the weaknesses we logged on the bench: Benched as a partial run until the full 50-task batch completes; Region-locked: unavailable across the EU/EEA/UK/CH — access depends on where you are.

How does Goldie Bench score Claude Fable 5 vs Fugu Ultra 1.1?

Every demo on this page was built by Julian Goldie inside the Agent Operating System — same fixed prompt for both models, one shot, single HTML file out. Each result gets a 0–10 score on whether it ran, how close it hit the brief, and how good it looked. The highest score on each task gets gold; second gets silver; third gets bronze. See methodology for full provenance.

Related comparisons

Other head-to-heads using the same scoring system:

Full model pages: Claude Fable 5 · Fugu Ultra 1.1 · back to the leaderboard