Gemini 2.5 Flash vs Gemini 3 Flash Preview vs Grok 4.20 (Reasoning)
Gemini 3 Flash Preview comes out ahead, 73 to 68 and 68 on our weighted score, though Gemini 2.5 Flash is 24% cheaper per token.
GoogleGemini 2.5 Flash
68/100- ECI140.8
- Price$0.30 / $2.50
- Context1.05M
- Our pickGoogle
Gemini 3 Flash Preview
73/100- ECI151.8
- Price$0.50 / $3.00
- Context1.05M
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 Gemini 2.5 Flash (68). Gemini 2.5 Flash wins on price. 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 · Gemini 2.5 Flash 140.8
- Lowest priceGemini 2.5 FlashGemini 2.5 Flash $0.85 · Gemini 3 Flash Preview $1.13 · Grok 4.20 (Reasoning) $1.56 per 1M tokens (3:1 blend)
- Longest contextGemini 2.5 Flash and Gemini 3 Flash PreviewGemini 2.5 Flash 1,048,576 · Gemini 3 Flash Preview 1,048,576 · Grok 4.20 (Reasoning) 1,000,000 tokens
- Widest inputsGemini 2.5 Flash and Gemini 3 Flash PreviewGemini 2.5 Flash: Text, Images, PDFs, Audio, Video · Gemini 3 Flash Preview: Text, Images, PDFs, Audio, Video · Grok 4.20 (Reasoning): Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Gemini 2.5 Flash | Gemini 3 Flash Preview | Grok 4.20 (Reasoning) |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 67 | 80 | 81 |
| Price | 25% | 53 | 47 | 41 |
| Inputs & features | 15% | 100 | 100 | 80 |
| Context window | 10% | 61 | 61 | 60 |
| Overall | 100% | 68/100 | 73/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Gemini 2.5 FlashGoogle | Gemini 3 Flash PreviewGoogle | Grok 4.20 (Reasoning)xAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 140.8 | 151.8 | 152.0 (best) |
| ECI rank | #97 of 148 | #43 of 148 | #41 of 148 (best) |
| GPQA DiamondGraduate-level science questions | — | 89.4% (best) | 89.3% |
| FrontierMath Tiers 1–3Research-level mathematics | — | 51.2% (best) | 44.9% |
| OTIS Mock AIME 2024–2025Competition mathematics | — | 95.6% (best) | 92.2% |
| SWE-bench VerifiedFixing real GitHub issues | — | 75.4% | — |
| SimpleQA VerifiedShort factual questions | — | 66.8% (best) | 30.2% |
| Price per million tokens | |||
| Input | $0.30 (best) | $0.50 | $1.25 |
| Output | $2.50 (best) | $3.00 | $2.50 (best) |
| Cached input | $0.03 (best) | $0.05 | $0.20 |
| Blended (3:1) | $0.85 (best) | $1.13 | $1.56 |
| Long-context rate | Same rate | Same rate | Over 200K: $2.50 / $5.00 |
| Price source | Official Google API | Official Google API | Official xAI API |
| Limits | |||
| Context window | 1,048,576 tokens (best) | 1,048,576 tokens (best) | 1,000,000 tokens |
| Max output | 65,536 tokens (best) | 65,536 tokens (best) | 30,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | Yes |
| Audio | Yes | Yes | No |
| Video | Yes | Yes | No |
| Reasoning | Yes | Yesminimal · low · medium · high | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | gemini-2.5-flash | gemini-3-flash-preview | grok-4.20-0309-reasoning |
| API providers | 22 (best) | 20 | 11 |
| Released | Jun 17, 2025 | Dec 17, 2025 | Mar 9, 2026 |
| Knowledge cutoff | Jan 2025 | Jan 2025 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Gemini 2.5 Flash$8.00
- Gemini 3 Flash Preview$11.00
- Grok 4.20 (Reasoning)$17.50
Which should you choose?
Which is better: Gemini 2.5 Flash, Gemini 3 Flash Preview 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 Gemini 2.5 Flash (68). Gemini 2.5 Flash wins on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Gemini 2.5 Flash, Gemini 3 Flash Preview or Grok 4.20 (Reasoning)?
Gemini 2.5 Flash is cheaper at $0.30 input / $2.50 output per million tokens (official Google API price). Gemini 3 Flash Preview costs $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). At a typical mix of three input tokens to one output token, that is $0.85 per million tokens for Gemini 2.5 Flash versus $1.13 for Gemini 3 Flash Preview (1.3× as much) and $1.56 for Grok 4.20 (Reasoning) (1.8× 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 Gemini 2.5 Flash 140.8 (#97 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.
Which is better for coding?
There are no published SWE-bench Verified results for Gemini 2.5 Flash 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 2.5 Flash and Gemini 3 Flash Preview have the largest context windows (1,048,576 and 1,048,576 tokens), against 1,000,000 for Grok 4.20 (Reasoning). Maximum output per response: Gemini 2.5 Flash up to 65,536, Gemini 3 Flash Preview up to 65,536, Grok 4.20 (Reasoning) up to 30,000 tokens.
Which can read images, PDFs, audio or video?
Gemini 2.5 Flash accepts text, images, PDFs, audio and video; Gemini 3 Flash Preview accepts text, images, PDFs, audio and video; Grok 4.20 (Reasoning) accepts text, images and PDFs. Gemini 2.5 Flash handles the widest range of inputs.
Are any of these open source?
No. Gemini 2.5 Flash, Gemini 3 Flash Preview 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; Gemini 2.5 Flash came out Jun 17, 2025. Knowledge cutoff: Gemini 2.5 Flash Jan 2025, Gemini 3 Flash Preview Jan 2025.
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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