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Step 5 PreviewClaude Fable 5.1 vs Gemini 3.8 Flash
- Claude Fable 5.1 rates higher on LMArena’s text leaderboard: 1513 against 1498.
- Gemini 3.8 Flash is cheaper: $0.82 / $4.13 per million input / output tokens, against $10 / $50 for Claude Fable 5.1.
- On the 10 Vals AI benchmarks both have taken, Claude Fable 5.1 wins 9 and Gemini 3.8 Flash wins 1 (Claude Fable 5.1: Terminal-Bench 4.0, Vibe Code Bench, LiveCodeBench).
Side by side
Models (2/6)
- Claude Fable 5.1
- Gemini 3.8 Flash
| Benchmark | Claude Fable 5.1 | Gemini 3.8 Flash |
|---|---|---|
| The model | ||
| Lab | Anthropic | |
| Released | 2026-09-01 | 2026-09-02 |
| Weights | Proprietary | Proprietary |
| Context window | 1M | 1M |
| Input, per 1M tokens | $10 | $0.82 |
| Output, per 1M tokens | $50 | $4.13 |
| LMArena, people’s votes | ||
| LMArena TextMillions of people compare two anonymous models side by side and vote for the better answer | 1513#3 of 351 | 1498#8 of 351 |
| LMArena WebDevPeople ask two anonymous models to build the same web app, try both and vote for the better one | 1743#5 of 124 | 1585#36 of 124 |
| LMArena VisionSide-by-side votes on prompts that include an image | 1320#4 of 146 | 1315#7 of 146 |
| LMArena CodingLMArena’s text votes on prompts that ask for code | 1531#7 of 346 | 1508#17 of 346 |
| LMArena MathLMArena’s text votes on math prompts | 1532#3 of 339 | 1532#4 of 339 |
| LMArena Creative writingLMArena’s text votes on stories, poems and other creative writing | 1510#3 of 349 | 1489#8 of 349 |
| LMArena Hard promptsLMArena’s text votes on the hardest prompts | 1528#3 of 351 | 1509#9 of 351 |
| LMArena Instruction followingLMArena’s text votes on prompts with specific instructions to follow | 1519#4 of 351 | 1492#11 of 351 |
| Vals AI, overall | ||
| Vals IndexVals AI’s headline score | — | 55.95%#15 of 27 |
| Vals AI, coding | ||
| Terminal-Bench 4.0Frontier-difficulty tasks an agent completes in a real terminal | 58.08%#5 of 55 | 19.70%#31 of 55 |
| SWE-benchReal GitHub issues from open-source projects | — | 80.00%#23 of 85 |
| Vibe Code BenchBuilding complete web apps from a plain-language brief, graded on whether the app works | 90.26%#6 of 115 | 78.65%#29 of 115 |
| Code MigrationRewriting working programs in a new language, graded on whether the new program still passes its tests | — | 38.65%#22 of 28 |
| LiveCodeBenchFresh competitive programming problems, collected after models’ training cut-offs to avoid contamination | 90.52%#1 of 143 | 89.48%#3 of 143 |
| Vals AI, finance | ||
| Finance AgentThe core tasks of a financial analyst, done as an agent with research tools | — | 65.76%#5 of 31 |
| Finance IndexVals AI’s composite of finance tasks | — | 60.46%#9 of 31 |
| Tax Agent BenchAgentic research into US corporate tax questions | 49.19%#2 of 76 | 32.12%#21 of 76 |
| Vals AI, law | ||
| Legal IndexVals AI’s composite of legal tasks | — | 69.78%#14 of 28 |
| Legal Research BenchAgentic US legal research | 55.29%#3 of 85 | 38.94%#34 of 85 |
| Vals AI, medicine | ||
| MedCodeAssigning the right medical billing codes from clinical notes | 53.51%#8 of 107 | 48.13%#31 of 107 |
| Vals AI, reasoning | ||
| GPQA DiamondGraduate-level questions in biology, physics and chemistry that experts answer well and search does not | 93.43%#9 of 138 | 94.44%#4 of 138 |
| MMLU-ProHarder, reasoning-focused multiple choice across 14 subjects, from law to engineering | 92.38%#1 of 138 | 90.22%#5 of 138 |
| MMMUCollege-level questions that need both an image and text | 90.64%#1 of 93 | 89.08%#4 of 93 |
| Terminal-Bench ScienceExpert-written scientific research workflows, run by an agent in a terminal | 40.00%#6 of 42 | 8.57%#19 of 42 |
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Questions
Which is better, Claude Fable 5.1 or Gemini 3.8 Flash?
Claude Fable 5.1 rates higher on LMArena’s text leaderboard: 1513 against 1498. Gemini 3.8 Flash is cheaper: $0.82 / $4.13 per million input / output tokens, against $10 / $50 for Claude Fable 5.1. On the 10 Vals AI benchmarks both have taken, Claude Fable 5.1 wins 9 and Gemini 3.8 Flash wins 1 (Claude Fable 5.1: Terminal-Bench 4.0, Vibe Code Bench, LiveCodeBench).
Which is cheaper, Claude Fable 5.1 or Gemini 3.8 Flash?
Gemini 3.8 Flash is cheaper: $0.82 / $4.13 per million input / output tokens, against $10 / $50 for Claude Fable 5.1.