Gemini 3.1 Pro vs Gemini 3.8 Flash
Gemini 3.8 Flash leads overall, C- to F. Gemini 3.1 Pro is about 1.5x cheaper per task. By suite, Gemini 3.8 Flash takes real-world issues (C- to D+) and spec planning (D+ to F). Take Gemini 3.1 Pro anyway when you want the side that is cheaper per task and faster on real-world issues.Measured
Each agent graded on the same private suites, running headless through its own tools. Advantages are oriented so a win is a win, whichever way the metric runs.
Verdict: Gemini 3.8 Flash vs Gemini 3.1 Pro
Gemini 3.8 Flash leads overall, C- to F. By suite: Gemini 3.8 Flash takes real-world issues, C- to D+ (60% vs 53% capability); Gemini 3.8 Flash takes spec planning, D+ to F (50% vs 21% capability); Gemini 3.8 Flash takes vibe coding, C- to F (56% vs 27% capability). Gemini 3.1 Pro used 15.9% of Google AI Pro's weekly limit per pass, $0.038 per task at the listed price. Gemini 3.8 Flash used 23.7% of Google AI Pro's weekly limit per pass, $0.057 per task at the listed price. Per task, Gemini 3.1 Pro is about 1.5x cheaper ($0.038 vs $0.057). Gemini 3.1 Pro is faster on real-world issues: a median task takes 4m 53s against 5m 21s. Both finished every task on it. Reasons to pick Gemini 3.1 Pro anyway: it is cheaper per task ($0.038 vs $0.057) and it is faster on real-world issues (4m 53s vs 5m 21s median).
Changed since W39: Gemini 3.1 Pro: real-world issues usage 9.8% to 14.8% of the weekly limit, spec planning usage 0.9% to 1.1% of the weekly limit, vibe coding usage 1.0% to 0.7% of the weekly limit; Gemini 3.8 Flash: real-world issues F to C-, real-world issues usage 18.0% to 21.9% of the weekly limit, spec planning usage 2.0% to 1.8% of the weekly limit, vibe coding D+ to C-, vibe coding usage 1.2% to 1.1% of the weekly limit.
| Dimension | Gemini 3.1 Pro | Gemini 3.8 Flash | Advantage |
|---|---|---|---|
| Capability | 53% | 60% | +7% (Gemini 3.8 Flash leads) |
| Median task time | 4m 53s | 5m 21s | 28s faster (Gemini 3.1 Pro leads) |
| Approx. task cost | $0.045 / task | $0.067 / task | $0.022 / task lower (Gemini 3.1 Pro leads) |
Gemini 3.1 Pro: 14.8% of Google AI Pro (88.9% / 5h, 14.8% / 1w) per run. Its weekly limit holds 6 of the week's 33.6 5h windows. Gemini 3.8 Flash: 21.9% of Google AI Pro (131.3% / 5h, 21.9% / 1w) per run. Its weekly limit holds 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | Gemini 3.1 Pro | Gemini 3.8 Flash | Advantage |
|---|---|---|---|
| Capability | 21% | 50% | +29% (Gemini 3.8 Flash leads) |
| Median task time | 1m 46s | 3m 0s | 1m 15s faster (Gemini 3.1 Pro leads) |
| Approx. task cost | $0.013 / task | $0.021 / task | $0.009 / task lower (Gemini 3.1 Pro leads) |
Gemini 3.1 Pro: 1.1% of Google AI Pro (6.5% / 5h, 1.1% / 1w) per run. Its weekly limit holds 6 of the week's 33.6 5h windows. Gemini 3.8 Flash: 1.8% of Google AI Pro (11.0% / 5h, 1.8% / 1w) per run. Its weekly limit holds 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | Gemini 3.1 Pro | Gemini 3.8 Flash | Advantage |
|---|---|---|---|
| Capability | 27% | 56% | +29% (Gemini 3.8 Flash leads) |
| Median task time | 4m 38s | 7m 51s | 3m 13s faster (Gemini 3.1 Pro leads) |
| Approx. task cost | $0.034 / task | $0.048 / task | $0.014 / task lower (Gemini 3.1 Pro leads) |
Gemini 3.1 Pro: 0.7% of Google AI Pro (4.4% / 5h, 0.7% / 1w) per good solve. Its weekly limit holds 6 of the week's 33.6 5h windows. Gemini 3.8 Flash: 1.1% of Google AI Pro (6.3% / 5h, 1.1% / 1w) per good solve. Its weekly limit holds 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
Grades and deltas are comparable only within a suite version. See methodology.
Frequently asked questions
Which is better for coding, Gemini 3.1 Pro or Gemini 3.8 Flash?
Gemini 3.8 Flash clears higher: tier 4 of 5 versus tier 3 for Gemini 3.1 Pro on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-28.
Which is cheaper per task, Gemini 3.1 Pro or Gemini 3.8 Flash?
Gemini 3.1 Pro used 15.9% of Google AI Pro's weekly limit per pass, $0.038 per task at the listed price. Gemini 3.8 Flash used 23.7% of Google AI Pro's weekly limit per pass, $0.057 per task at the listed price. Per task, Gemini 3.1 Pro is about 1.5x cheaper ($0.038 vs $0.057).