In short
How they differ.
Worked out from the figures below. Prices and specs are the makers' own, read Oct 20, 2026.
- No independent board we follow ranks both models yet.
Side by side
The specs.
| Claude Mythos 5.1 | Gemini 3.8 Flash | |
|---|---|---|
| Made by | Anthropic · US | Google · US |
| Released | Sep 1, 2026 | Sep 2, 2026 |
| Price per 1M tokens | No public price | $0.75 in / $3.75 out (introductory price) |
| Context window | Not stated | 1M |
| Takes in | Not stated | text, image, video, audio, pdf |
| Download and run it yourself | No | No |
| Size | Not published | Not published |
| Maker says | “Our most capable model for cybersecurity and biology research.” | “Gemini 3.8 Flash is our most intelligent Flash model, engineered for long-horizon software engineering, autonomous agents, and complex enterprise workflows—all with the speed and cost efficiency of Flash.” |
| Sources | Prices, Oct 20, 2026 · Description | Prices, Oct 20, 2026 · Description |
Independent tests
Where they place.
Position on each board we follow (1 is best). Epoch AI's and Vectara's scores are shown; the other boards are linked for their own figures.
| Board | Claude Mythos 5.1 | Gemini 3.8 Flash |
|---|---|---|
| Epoch Capabilities IndexEpoch AI, Oct 20, 2026 | Not listed | #19157.2 |
| LMArena textLMArena, Oct 15, 2026 | Not listed | #9 |
| LMArena creative writingLMArena, Oct 15, 2026 | Not listed | #7 |
| LMArena mathLMArena, Oct 15, 2026 | Not listed | #4 |
| LMArena visionLMArena, Oct 19, 2026 | Not listed | #12 |
| LMArena Agent ArenaLMArena, Oct 19, 2026 | Not listed | #15 |
| Humanity's Last ExamScale AI | Not listed | #8 |
| SWE-Bench ProScale AI, Sep 22, 2026 | Not listed | #12 |
| Remote Labor IndexScale AI | Not listed | #7 |
| Vals IndexVals AI, Oct 19, 2026 | Not listed | #13 |
| GPQA Diamond (run by Vals AI, archived)Vals AI, Sep 1, 2026 | Not listed | #4 |
| MMMU Pro (run by Vals AI, archived)Vals AI, Sep 1, 2026 | Not listed | #4 |
| CUA-bench (games)Vals AI, Oct 13, 2026 | Not listed | #9 |
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