Gemini 3.8 Flash vs GPT-6 Luna
Gemini 3.8 Flash leads overall, C- to D. By suite, real-world issues is even at C- and spec planning is even at D+. Take GPT-6 Luna anyway when you want the side that is faster on real-world issues. Both agents run the same private suite cut headless through their own tools, each on its own subscription.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: GPT-6 Luna vs Gemini 3.8 Flash
Gemini 3.8 Flash leads overall, C- to D. By suite: real-world issues is even at C- (60% vs 57% capability); spec planning is even at D+ (50% vs 55% capability); Gemini 3.8 Flash takes vibe coding, C- to F (56% vs 31% capability). Gemini 3.8 Flash used 23.7% of Google AI Pro's weekly limit per pass, $0.057 per task at the listed price. GPT-6 Luna used <1% of ChatGPT Plus's weekly limit per pass; at the ~$100 tier the board defaults to that is an estimated ~<0.2% of ChatGPT Pro 5x's weekly limit (est). GPT-6 Luna is faster on real-world issues: a median task takes 1m 4s against 5m 21s. Both finished every task on it. Reasons to pick GPT-6 Luna anyway: it is faster on real-world issues (1m 4s vs 5m 21s median).
Changed since W39: 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; GPT-6 Luna: real-world issues D+ to C-, spec planning C- to D+.
| Dimension | Gemini 3.8 Flash | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 60% | 57% | +3% (Gemini 3.8 Flash leads) |
| Median task time | 5m 21s | 1m 4s | 4m 16s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.067 / task | not measured | - |
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. GPT-6 Luna: under 1% of ChatGPT Plus (2.0% / 5h) per run. Its weekly limit holds about 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 3.8 Flash | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 50% | 55% | +4% (GPT-6 Luna leads) |
| Median task time | 3m 0s | 1m 20s | 1m 40s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.021 / task | <$0.011 / task | $0.010 / task lower (GPT-6 Luna leads) |
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. GPT-6 Luna: under 1% of ChatGPT Plus per run. Its weekly limit holds about 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 3.8 Flash | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 56% | 31% | +25% (Gemini 3.8 Flash leads) |
| Median task time | 7m 51s | 1m 24s | 6m 27s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.048 / task | <$0.046 / task | $0.002 / task lower (GPT-6 Luna leads) |
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. GPT-6 Luna: under 1% of ChatGPT Plus per good solve. Its weekly limit holds about 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 3.8 Flash or GPT-6 Luna?
Gemini 3.8 Flash clears higher: tier 4 of 5 versus tier 2 for GPT-6 Luna on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-27.
Which is cheaper per task, Gemini 3.8 Flash or GPT-6 Luna?
Gemini 3.8 Flash used 23.7% of Google AI Pro's weekly limit per pass, $0.057 per task at the listed price. GPT-6 Luna used <1% of ChatGPT Plus's weekly limit per pass; at the ~$100 tier the board defaults to that is an estimated ~<0.2% of ChatGPT Pro 5x's weekly limit (est).