Gemini 3.8 Flash vs Claude Fable 5.1
Claude Fable 5.1 leads overall, B- to C-. Gemini 3.8 Flash is about 1.7x cheaper per task. By suite, Claude Fable 5.1 takes real-world issues (B+ to C-) and spec planning (C+ to D+). Take Gemini 3.8 Flash anyway when you want the side that is cheaper per task.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: Claude Fable 5.1 vs Gemini 3.8 Flash
Claude Fable 5.1 leads overall, B- to C-. By suite: Claude Fable 5.1 takes real-world issues, B+ to C- (87% vs 60% capability); Claude Fable 5.1 takes spec planning, C+ to D+ (71% vs 50% capability); Claude Fable 5.1 takes vibe coding, C+ to C- (74% vs 56% 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. Claude Fable 5.1 used 8% of Claude Max 5x's weekly limit per pass, $0.097 per task at the listed price. Per task, Gemini 3.8 Flash is about 1.7x cheaper ($0.057 vs $0.097). Claude Fable 5.1 is faster on real-world issues: a median task takes 3m 38s against 5m 21s. Both finished every task on it. Reasons to pick Gemini 3.8 Flash anyway: it is cheaper per task ($0.057 vs $0.097).
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; Claude Fable 5.1: real-world issues D+ to B+, real-world issues usage 7% to 5% of the weekly limit, spec planning usage 4% to 3% of the weekly limit, vibe coding C- to C+, vibe coding usage 0.6% to 0.4% of the weekly limit.
| Dimension | Gemini 3.8 Flash | Claude Fable 5.1 | Advantage |
|---|---|---|---|
| Capability | 60% | 87% | +27% (Claude Fable 5.1 leads) |
| Median task time | 5m 21s | 3m 38s | 1m 43s faster (Claude Fable 5.1 leads) |
| Approx. task cost | $0.067 / task | $0.077 / task | $0.010 / task lower (Gemini 3.8 Flash leads) |
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. Claude Fable 5.1: 64.0% of Claude Max 5x (64.0% / 5h, 5.0% / 1w) per run. Its weekly limit holds about 13.8 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 | Claude Fable 5.1 | Advantage |
|---|---|---|---|
| Capability | 50% | 71% | +20% (Claude Fable 5.1 leads) |
| Median task time | 3m 0s | 8m 55s | 5m 55s faster (Gemini 3.8 Flash leads) |
| Approx. task cost | $0.021 / task | $0.172 / task | $0.151 / task lower (Gemini 3.8 Flash 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. Claude Fable 5.1: 33.0% of Claude Max 5x (33.0% / 5h, 3.0% / 1w) per run. Its weekly limit holds about 13.8 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 | Claude Fable 5.1 | Advantage |
|---|---|---|---|
| Capability | 56% | 74% | +18% (Claude Fable 5.1 leads) |
| Median task time | 7m 51s | 4m 14s | 3m 37s faster (Claude Fable 5.1 leads) |
| Approx. task cost | $0.048 / task | $0.092 / task | $0.044 / task lower (Gemini 3.8 Flash 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. Claude Fable 5.1: 4.2% of Claude Max 5x (4.2% / 5h, 0.4% / 1w) per good solve. Its weekly limit holds about 13.8 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 Claude Fable 5.1?
Both clear tier 4 of 5, but Claude Fable 5.1 scores higher on capability: 87% versus 60% 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 Claude Fable 5.1?
Gemini 3.8 Flash used 23.7% of Google AI Pro's weekly limit per pass, $0.057 per task at the listed price. Claude Fable 5.1 used 8% of Claude Max 5x's weekly limit per pass, $0.097 per task at the listed price. Per task, Gemini 3.8 Flash is about 1.7x cheaper ($0.057 vs $0.097).