Head-to-head comparison
Claude Fable 5.1 (Anthropic) and Grok 4.20 Multi-Agent (xAI) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.
Snapshot as of 3 September 2026
As of 3 September 2026, Claude Fable 5.1 holds the stronger ModelCap Index position (#2 vs #12); Grok 4.20 Multi-Agent is 20× cheaper per output token ($2.50/1M vs $50.00/1M); and Grok 4.20 Multi-Agent offers the longer context window (2M vs 1M tokens).
Evidence: 2 public benchmark observations across 2 boards · 2 public benchmark observations across 2 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.
Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.
Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.
Claude Fable 5.1 ranks higher on the ModelCap Index as of 3 September 2026: #2 against #12. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it.
Grok 4.20 Multi-Agent is cheaper on output tokens: $2.50/1M against $50.00/1M. Input tokens are $10.00/1M for Claude Fable 5.1 and $1.25/1M for Grok 4.20 Multi-Agent. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens.
Grok 4.20 Multi-Agent has the larger context window: 2M tokens against 1M.
The two models do not share a coding benchmark board on ModelCap yet, so no head-to-head coding score is published; the ModelCap Index position is the closest overall signal.
Claude Fable 5.1: API only. Grok 4.20 Multi-Agent: API only. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.
ModelCap currently lists 4 API providers for Claude Fable 5.1 and 1 for Grok 4.20 Multi-Agent, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.
Every figure comes from the sealed ModelCap dataset published 3 September 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.