Claude Fable 5 vs Grok

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 Grok, side by side, on 47 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.

Grok · Used for real-time content workflows where the model needs current X timeline context. Standalone bench scoring pending.

Where Claude Fable 5 beat Grok

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 Grok beat Claude Fable 5

The tasks where I gave Grok 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 43 scored shared tasks, the averages are essentially tied — Claude Fable 5 8.07 vs Grok 8.09. This isn't the comparison where one wins; it's the comparison where you pick based on context, pricing, and what you're actually trying to ship.

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 Grok 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, workflows that need live x / twitter context → Grok. That's the same setup I run for the 4,000+ founders inside the AI Profit Boardroom.

FAQ — Claude Fable 5 vs Grok

Which is better, Claude Fable 5 or Grok?

On Goldie Bench, Claude Fable 5 averages 8.07/10 across the shared tasks, with 4 gold, 2 silver, 1 bronze overall. Grok averages 8.09/10, with 5 gold, 1 silver, 1 bronze. Claude Fable 5 wins the head-to-head 20–17.

How much does Claude Fable 5 cost vs Grok?

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. Grok: Bundled with X (Twitter) Premium subscription — no per-token bill for end users, no individual API pricing for the chat product.

What's the context window for Claude Fable 5 vs Grok?

Claude Fable 5 has a 200,000 tokens (1M with extended thinking) context window. Grok has a 256,000 tokens context window.

When should I pick Claude Fable 5 over Grok?

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 Grok over Claude Fable 5?

Pick Grok for: Workflows that need live X / Twitter context; Snappy prompts where latency matters; Researchers comparing X-native models against the rest of the field. The trade-off is the weaknesses we logged on the bench: 13 demos on the bench but zero have curated 0–10 verdicts yet — currently unranked; API access is gated behind X Premium, awkward for backend agent loops.

How does Goldie Bench score Claude Fable 5 vs Grok?

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 · Grok · back to the leaderboard