Gemini 3.8 Flash vs GPT-6 Luna
Both grade D overall. GPT-6 Luna is about 20x cheaper per task. By suite, GPT-6 Luna takes real-world issues (D+ to F) and spec planning (C- to D+). 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
Both grade D overall. By suite: GPT-6 Luna takes real-world issues, D+ to F (50% vs 28% capability); GPT-6 Luna takes spec planning, C- to D+ (61% vs 50% capability); Gemini 3.8 Flash takes vibe coding, D+ to F (52% vs 33% capability). Gemini 3.8 Flash used 19.9% of Google AI Pro's weekly limit per pass, $0.048 per task at the listed price. GPT-6 Luna used 1% of ChatGPT Plus's weekly limit per pass, $0.002 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~0.2% of ChatGPT Pro 5x's weekly limit (est, about $0.002 per task). Per task, GPT-6 Luna is about 20x cheaper ($0.002 vs $0.048). GPT-6 Luna is faster on real-world issues: a median task takes 1m 0s against 3m 11s. Both finished every task on it.
Changed since W38: Gemini 3.8 Flash: real-world issues D+ to F, real-world issues usage 18.4% to 18.0% of the weekly limit, spec planning D to D+, spec planning usage 1.7% to 2.0% of the weekly limit, vibe coding C- to D+, vibe coding usage 1.0% to 1.2% of the weekly limit.
| Dimension | Gemini 3.8 Flash | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 28% | 50% | +22% (GPT-6 Luna leads) |
| Median task time | 3m 11s | 1m 0s | 2m 11s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.055 / task | $0.003 / task | $0.052 / task lower (GPT-6 Luna leads) |
Gemini 3.8 Flash: 18.0% of Google AI Pro (107.8% / 5h, 18.0% / 1w) per run. Its weekly limit holds 6 of the week's 33.6 5h windows. GPT-6 Luna: 1.0% of ChatGPT Plus (1.0% / 5h, 1.0% / 1w) 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% | 61% | +10% (GPT-6 Luna leads) |
| Median task time | 2m 23s | 1m 8s | 1m 15s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.023 / task | <$0.011 / task | $0.011 / task lower (GPT-6 Luna leads) |
Gemini 3.8 Flash: 2.0% of Google AI Pro (11.7% / 5h, 2.0% / 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 | 52% | 33% | +19% (Gemini 3.8 Flash leads) |
| Median task time | 6m 42s | 1m 37s | 5m 5s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.054 / task | not measured | - |
Gemini 3.8 Flash: 1.2% of Google AI Pro (7.0% / 5h, 1.2% / 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 (0.4% / 5h) 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?
GPT-6 Luna clears higher: tier 2 of 5 versus tier 0 for Gemini 3.8 Flash on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-20.
Which is cheaper per task, Gemini 3.8 Flash or GPT-6 Luna?
Gemini 3.8 Flash used 19.9% of Google AI Pro's weekly limit per pass, $0.048 per task at the listed price. GPT-6 Luna used 1% of ChatGPT Plus's weekly limit per pass, $0.002 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~0.2% of ChatGPT Pro 5x's weekly limit (est, about $0.002 per task). Per task, GPT-6 Luna is about 20x cheaper ($0.002 vs $0.048).