Estimating Fable and Sol model sizes

I'll pull the linked source so the paragraphs stay grounded in what was actually claimed about Fable and Sol sizes.Researcher **@anpaure** published **Frontier model size estimates**, an interactive chart of implied total parameters for current frontier models, and shared it on X. On Hacker News the link sat at **7 points** with **0 comments**. The two headline figures are **Claude Fable 5** at a **model estimate of 4.5T** parameters and **GPT-5.6 Sol** at **3.1T**.

The page does not treat those numbers as single opaque guesses. It combines audited capability signals from the **Artificial Analysis Intelligence Index** and the **Epoch Capabilities Index**, uses **No-CoT Time Horizon** as the primary parameter-scaling branch, and treats API price and compute as lower-weight checks. For **Fable** and **Sol** specifically, the **public estimate** is the **geometric mean** of parameter-count forecasts from a **20-person poll** of researchers and engineers. The forest plot shows a wider **weighted factor range** for Fable (**3.2–6.6T**, public estimate **4.4T**) than for Sol (**2.9–3.4T**, public estimate **3.2T**), so Sol’s band is tighter around its point estimate.

For engineers building on **Claude** and **Codex**, parameter scale is a proxy for latency, cost, and when a smaller tier is enough. If Sol is ~**3.1T** and Fable ~**4.5T**, routing, caching, and agent budgets should not treat the two flagships as interchangeable black boxes. The poll-plus-evidence method is reproducible: you can reweight channels and see which inputs move the estimate.

On the same scale, **Claude Opus 5** sits at **3.0T**, disclosed **Kimi K3** at **2.8T**, **Claude Opus 4.8** at **2.7T**, **GPT-5.5** at **2.3T**, **GPT-5.6 Terra** at **2.1T**, **Claude Sonnet 5** at **1.6T**, and both **Grok 4.5** (disclosed) and **GPT-5.6 Luna** at **1.5T**. That puts Fable above the rest of the chart and Sol roughly in the Opus 5 / Kimi K3 band, with OpenAI’s family clearly tiered (**Sol > Terra > Luna**).

Treat the numbers as estimates, not vendor specs. Watch the **repo** and chart for poll updates, factor reweights, and any official disclosures that pin Fable or Sol the way **Kimi K3** and **Grok 4.5** already are.