In short
How they differ.
Worked out from the figures below. Prices and specs are the makers' own, read Oct 20, 2026.
- Gemini 3.8 Flash is cheaper per output token: $3.75 against $10 per million tokens, so Claude Sonnet 5.5 costs 2.7 times as much.
- Gemini 3.8 Flash reads more at once: a context window of 1M tokens against 1M.
- On the 6 independent boards that rank both, Claude Sonnet 5.5 places higher on 5 and Gemini 3.8 Flash on 1.
Side by side
The specs.
| Claude Sonnet 5.5 | Gemini 3.8 Flash | |
|---|---|---|
| Made by | Anthropic · US | Google · US |
| Released | Sep 28, 2026 | Sep 2, 2026 |
| Price per 1M tokens | $2 in / $10 out | $0.75 in / $3.75 out (introductory price) |
| Context window | 1M | 1M |
| Takes in | text, image | text, image, video, audio, pdf |
| Download and run it yourself | No | No |
| Size | Not published | Not published |
| Maker says | “High-performance model for coding and agents” | “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 Sonnet 5.5 | Gemini 3.8 Flash |
|---|---|---|
| Epoch Capabilities IndexEpoch AI, Oct 20, 2026 | #6164.45 | #19157.2 |
| LMArena textLMArena, Oct 15, 2026 | Not listed | #9 |
| LMArena creative writingLMArena, Oct 15, 2026 | Not listed | #7 |
| LMArena WebDevLMArena, Oct 19, 2026 | #3 | Not listed |
| LMArena mathLMArena, Oct 15, 2026 | #15 | #4 |
| LMArena visionLMArena, Oct 19, 2026 | Not listed | #12 |
| LMArena Agent ArenaLMArena, Oct 19, 2026 | #5 | #15 |
| Humanity's Last ExamScale AI | #6 | #8 |
| SWE-Bench ProScale AI, Sep 22, 2026 | #8 | #12 |
| Remote Labor IndexScale AI | Not listed | #7 |
| Vals IndexVals AI, Oct 19, 2026 | #1 | #13 |
| Terminal-Bench 4.0Vals AI, Oct 19, 2026 | #2 | Not listed |
| Vibe Code BenchVals AI, Oct 18, 2026 | #1 | Not listed |
| ProofBenchVals AI, Oct 12, 2026 | #1 | Not listed |
| 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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