Gemini 3 Flash Preview vs Claude Sonnet 3.5 v2 vs Grok 4.20 (Reasoning)
Gemini 3 Flash Preview comes out ahead, 73 to 68 and 44 on our weighted score, and it is the cheaper option too.
- Our pick
GoogleGemini 3 Flash Preview
73/100- ECI151.8
- Price$0.50 / $3.00
- Context1.05M
AnthropicClaude Sonnet 3.5 v2
44/100- ECI133.5
- Price$3.00 / $15.00
- Context200K
xAIGrok 4.20 (Reasoning)
68/100- ECI152.0
- Price$1.25 / $2.50
- Context1M
Gemini 3 Flash Preview is our pick
Gemini 3 Flash Preview is the better all-round choice, scoring 73/100 against Grok 4.20 (Reasoning) (68) and Claude Sonnet 3.5 v2 (44). It leads on price and inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGrok 4.20 (Reasoning)Capabilities Index (ECI): Grok 4.20 (Reasoning) 152.0 · Gemini 3 Flash Preview 151.8 · Claude Sonnet 3.5 v2 133.5
- Lowest priceGemini 3 Flash PreviewGemini 3 Flash Preview $1.13 · Grok 4.20 (Reasoning) $1.56 · Claude Sonnet 3.5 v2 $6.00 per 1M tokens (3:1 blend)
- Longest contextGemini 3 Flash PreviewGemini 3 Flash Preview 1,048,576 · Grok 4.20 (Reasoning) 1,000,000 · Claude Sonnet 3.5 v2 200,000 tokens
- Widest inputsGemini 3 Flash PreviewGemini 3 Flash Preview: Text, Images, PDFs, Audio, Video · Claude Sonnet 3.5 v2: Text, Images, PDFs · Grok 4.20 (Reasoning): Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Gemini 3 Flash Preview | Claude Sonnet 3.5 v2 | Grok 4.20 (Reasoning) |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 80 | 57 | 81 |
| Price | 25% | 47 | 13 | 41 |
| Inputs & features | 15% | 100 | 60 | 80 |
| Context window | 10% | 61 | 32 | 60 |
| Overall | 100% | 73/100 | 44/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Gemini 3 Flash PreviewGoogle | Claude Sonnet 3.5 v2Anthropic | Grok 4.20 (Reasoning)xAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 151.8 | 133.5 | 152.0 (best) |
| ECI rank | #43 of 148 | #119 of 148 | #41 of 148 (best) |
| GPQA DiamondGraduate-level science questions | 89.4% (best) | 55.3% | 89.3% |
| FrontierMath Tiers 1–3Research-level mathematics | 51.2% (best) | — | 44.9% |
| OTIS Mock AIME 2024–2025Competition mathematics | 95.6% (best) | 8.5% | 92.2% |
| SWE-bench VerifiedFixing real GitHub issues | 75.4% | — | — |
| SimpleQA VerifiedShort factual questions | 66.8% (best) | — | 30.2% |
| Price per million tokens | |||
| Input | $0.50 (best) | $3.00 | $1.25 |
| Output | $3.00 | $15.00 | $2.50 (best) |
| Cached input | $0.05 (best) | — | $0.20 |
| Blended (3:1) | $1.13 (best) | $6.00 | $1.56 |
| Long-context rate | Same rate | Same rate | Over 200K: $2.50 / $5.00 |
| Price source | Official Google API | Median of 1 providers | Official xAI API |
| Limits | |||
| Context window | 1,048,576 tokens (best) | 200,000 tokens | 1,000,000 tokens |
| Max output | 65,536 tokens (best) | 8,192 tokens | 30,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | Yes |
| Audio | Yes | No | No |
| Video | Yes | No | No |
| Reasoning | Yesminimal · low · medium · high | No | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | No | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | gemini-3-flash-preview | — | grok-4.20-0309-reasoning |
| API providers | 20 (best) | 1 | 11 |
| Released | Dec 17, 2025 | Oct 22, 2024 | Mar 9, 2026 |
| Knowledge cutoff | Jan 2025 | Apr 30, 2024 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Gemini 3 Flash Preview$11.00
- Claude Sonnet 3.5 v2$60.00
- Grok 4.20 (Reasoning)$17.50
Which should you choose?
Which is better: Gemini 3 Flash Preview, Claude Sonnet 3.5 v2 or Grok 4.20 (Reasoning)?
Gemini 3 Flash Preview is the better all-round choice, scoring 73/100 against Grok 4.20 (Reasoning) (68) and Claude Sonnet 3.5 v2 (44). It leads on price and inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Gemini 3 Flash Preview, Claude Sonnet 3.5 v2 or Grok 4.20 (Reasoning)?
Gemini 3 Flash Preview is cheaper at $0.50 input / $3.00 output per million tokens (official Google API price). Grok 4.20 (Reasoning) costs $1.25 input / $2.50 output per million tokens (official xAI API price); Claude Sonnet 3.5 v2 costs $3.00 input / $15.00 output per million tokens (median across 1 API provider). At a typical mix of three input tokens to one output token, that is $1.13 per million tokens for Gemini 3 Flash Preview versus $1.56 for Grok 4.20 (Reasoning) (1.4× as much) and $6.00 for Claude Sonnet 3.5 v2 (5.3× as much).
Which scores higher on benchmarks?
Grok 4.20 (Reasoning) scores higher on the Capabilities Index (ECI): Grok 4.20 (Reasoning) 152.0 (#41 of 148), Gemini 3 Flash Preview 151.8 (#43 of 148) and Claude Sonnet 3.5 v2 133.5 (#119 of 148). The confidence ranges of the top two overlap (149.3–154.4 vs 150.4–153.7), so treat the gap as small. On individual benchmarks: GPQA Diamond — Gemini 3 Flash Preview 89.4%, Grok 4.20 (Reasoning) 89.3%, Claude Sonnet 3.5 v2 55.3%; OTIS Mock AIME 2024–2025 — Gemini 3 Flash Preview 95.6%, Grok 4.20 (Reasoning) 92.2%, Claude Sonnet 3.5 v2 8.5%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Sonnet 3.5 v2 and Grok 4.20 (Reasoning) yet, so there is no like-for-like coding score. On overall capability, Grok 4.20 (Reasoning) leads, which tends to carry over to coding, but test on your own codebase. All three support tool calling for agent workflows.
Which has the bigger context window?
Gemini 3 Flash Preview has the largest context window at 1,048,576 tokens, against 1,000,000 for Grok 4.20 (Reasoning) and 200,000 for Claude Sonnet 3.5 v2. Maximum output per response: Gemini 3 Flash Preview up to 65,536, Claude Sonnet 3.5 v2 up to 8,192, Grok 4.20 (Reasoning) up to 30,000 tokens.
Which can read images, PDFs, audio or video?
Gemini 3 Flash Preview accepts text, images, PDFs, audio and video; Claude Sonnet 3.5 v2 accepts text, images and PDFs; Grok 4.20 (Reasoning) accepts text, images and PDFs. Gemini 3 Flash Preview handles the widest range of inputs.
Are any of these open source?
No. Gemini 3 Flash Preview, Claude Sonnet 3.5 v2 and Grok 4.20 (Reasoning) are proprietary and only available through APIs and apps.
Which is newer?
Grok 4.20 (Reasoning) is the newest, released Mar 9, 2026. Gemini 3 Flash Preview came out Dec 17, 2025; Claude Sonnet 3.5 v2 came out Oct 22, 2024. Knowledge cutoff: Gemini 3 Flash Preview Jan 2025, Claude Sonnet 3.5 v2 Apr 30, 2024.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
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