Standard Compute
Model comparison 2026

Claude Fable 5.1 vs Grok 4.20

Claude Fable 5.1
Anthropic · Frontier · Proprietary
$22/1M · 1M ctx
Grok 4.20
xAI · Frontier · Proprietary
$1.63/1M · 2M ctx

Community vote

Pick a winner in each dimension. You can change your vote any time.

Output Quality
Correctness and depth of what it produces
Agentic Ability
Tool calls, instruction-following, and multi-step tasks
Speed
Tokens per second and time-to-first-token
Value for money
How much capability you get per dollar
Reliability
Consistent results: fewer refusals, loops and format breaks

Specs and pricing side by side

Spec
Fable 5.1
Grok 4.20
Maker
Anthropic
xAI
Blended price / 1M
$22
$1.63
Input / output
$10 in · $50 out / 1M tokens
$1.25 in · $2.50 out / 1M tokens
Context window
1M
2M
Open weights
No
No
Tool use
Yes
Yes
Reasoning
Yes
Yes
Output Quality
9.7
8.6
Agentic Ability
9.7
8.0
Speed
6.7
7.6
Value for money
6.9
8.5
Reliability
9.6
8.5

Pricing and capabilities synced from the OpenRouter catalogue. Scores are editorial (0–10).

Verdict: Fable 5.1 or Grok 4.20?

Updated 2026-10-13

Choose Claude Fable 5.1 if you want teams already standardized on Fable that want the newest premium Claude. Choose Grok 4.20 if you want agents that genuinely need 2M tokens of context.

In our editorial scoring, Claude Fable 5.1 leads in 3 of five dimensions (output quality, agentic ability and reliability), while Grok 4.20 leads in 2. On price, Claude Fable 5.1 runs about $22 per 1M tokens (blended) and is proprietary; Grok 4.20 is about $1.63 and proprietary.

Where Fable 5.1 falls short
  • Opus 5.5 scores higher on Artificial Analysis and Terminal-Bench 4.0 at less than half the price
  • Slow: about 67 output tokens/s at max effort
Full Fable 5.1 breakdown →
Where Grok 4.20 falls short
  • Big context costs add up fast
  • Smaller ecosystem than GPT/Claude
Full Grok 4.20 breakdown →

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