Why Your Gemini Bill Doesn't Match the Model Names
tl;dr - Across roughly 3,300 paired skill-eval runs, Gemini 3.5 Flash cost $1.05 per task against Gemini 3.1 Pro's $0.66, for scores that were effectively identical: 88.6 versus 87.9.
The pricing is even stranger when you look at the actual task costs. Gemini 3.5 Flash and Gemini 4.5 Flash are separated by almost 8× in per-task cost, while Gemini 3.1 Pro comes in cheaper than both. The invoice does not appear to follow the naming hierarchy.
Where the numbers come from?
The benchmark ran every task twice, once with the relevant skill applied and once without, across four Gemini models in OpenHands, totaling roughly 800 tasks per model. Rather than relying on dashboard estimates, we pulled per-call token counts directly from agent session logs and computed costs using Google's published per-token prices. We then compared the resulting per-task costs across models.
