Is the most expensive AI model the smartest one? I put 23 models' capability scores next to their API prices to check. Short answer: no. The top model costs about half of what the runner-up costs, and a model at 5% of the top price lands within 13 points of it.
Capability scores come from the Epoch Capabilities Index (ECI) by Epoch AI, which combines dozens of benchmarks (math, coding, science, reasoning) into one scale. Prices are standard API list prices, checked October 4, 2026.
Models on the green line are the best-value frontier: no other model is both cheaper and more capable. Anything below the line costs more than a frontier model with the same or higher score.
The short version
| Pick | Model | ECI | 10,000 chat requests |
|---|---|---|---|
| Top capability | Claude Opus 5.5 | 167.3 | $182 |
| Best value | Claude Sonnet 5.5 | 165.2 | $91 |
| Cheap and strong | Gemini 3.8 Flash | 156.9 | $25 |
| Lowest price | DeepSeek V4 Flash | 154.5 | $9 |
A chat request is 1,500 input + 400 output tokens of English text. Costs include each model's tokenizer difference: Claude counts about 30% more tokens than GPT for the same text, and that is already in the numbers.
Three things that surprised me
1. The #1 model is not the most expensive. Claude Opus 5.5 (167.3) edges out GPT-6 Astra (166.5), and the two are within each other's margin of error. But Astra lists at $10 / $50 per million tokens against Opus's $4 / $20, so 10,000 chats cost $350 on Astra and $182 on Opus.
2. "Good enough" is very close to the top. Claude Sonnet 5.5 is 2.2 points under Opus for half the price. Gemini 3.8 Flash and DeepSeek V4 Flash sit 10–13 points below the top at 7–20× lower cost, which is plenty for classification, extraction, summaries and most chatbot traffic.
3. Some popular picks are off the line. Claude Fable 5.1 ($455 per 10k chats) and GPT-5.5 ($195) both score below Sonnet 5.5 ($91). Gemini 3.1 Pro ($74) scores below Gemini 3.8 Flash ($25). They may still win on a specific task, but if you use them by default, test the cheaper option first.
What about GPT-6 Sol?
Epoch hasn't scored GPT-6 Sol yet. On a different scale, the Artificial Analysis Intelligence Index (v4.3.2, max reasoning, Sept 30), GPT-6.1 Sol scores 51.8 vs GPT-6 Astra's 52.7, at a fifth of the price. If that holds on ECI, Sol would sit on the frontier next to Claude Sonnet 5.5, which has the same list price. It isn't on the chart because the scales differ.
Live version
The chart and table rebuild every day from Epoch's data and current list prices. You can switch between top capability, best value and cheapest views here:
👉 AI model capability vs price ranking (free, no sign-up)
Full write-up with the "expensive for what you get" table: Best value LLM, October 2026.
Capability scores: Epoch Capabilities Index by Epoch AI, used under CC BY 4.0. Prices: API list prices, no caching or batch discounts.
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