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Comparison · 3 models · Updated Oct 4, 2026

Gemini 3.5 Flash vs Gemini 3 Flash Preview vs Grok 4.20 (Reasoning)

Gemini 3 Flash Preview comes out ahead, 73 to 69 and 68 on our weighted score, and it is the cheaper option too.

  1. Google

    Gemini 3.5 Flash

    Released May 19, 2026

    69/100
    • ECI154.5
    • Price$1.50 / $9.00
    • Context1.05M
    Full specs Remove Gemini 3.5 Flash
  2. Our pick

    Google

    Gemini 3 Flash Preview

    Released Dec 17, 2025

    73/100
    • ECI151.8
    • Price$0.50 / $3.00
    • Context1.05M
    Full specs Remove Gemini 3 Flash Preview

  3. xAI

    Grok 4.20 (Reasoning)

    Released Mar 9, 2026

    68/100
    • ECI152.0
    • Price$1.25 / $2.50
    • Context1M
    Full specs Remove Grok 4.20 (Reasoning)
01 — Verdict

Gemini 3 Flash Preview is our pick

Gemini 3 Flash Preview is the better all-round choice, scoring 73/100 against Gemini 3.5 Flash (69) and Grok 4.20 (Reasoning) (68). It leads on price. Gemini 3.5 Flash wins on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityGemini 3.5 FlashCapabilities Index (ECI): Gemini 3.5 Flash 154.5 · Grok 4.20 (Reasoning) 152.0 · Gemini 3 Flash Preview 151.8
  • Lowest priceGemini 3 Flash PreviewGemini 3 Flash Preview $1.13 · Grok 4.20 (Reasoning) $1.56 · Gemini 3.5 Flash $3.38 per 1M tokens (3:1 blend)
  • Longest contextGemini 3.5 Flash and Gemini 3 Flash PreviewGemini 3.5 Flash 1,048,576 · Gemini 3 Flash Preview 1,048,576 · Grok 4.20 (Reasoning) 1,000,000 tokens
  • Widest inputsGemini 3.5 Flash and Gemini 3 Flash PreviewGemini 3.5 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
How the score is built
MeasureWeightGemini 3.5 FlashGemini 3 Flash PreviewGrok 4.20 (Reasoning)
CapabilityCapabilities Index (ECI)50%848081
Price25%254741
Inputs & features15%10010080
Context window10%616160
Overall100%69/10073/10068/100
02 — Side by side

Every spec in one table

Highlighted cells lead their row. Dashes mean the data is not published.

Gemini 3.5 Flash vs Gemini 3 Flash Preview vs Grok 4.20 (Reasoning) specifications side by side
SpecificationGemini 3.5 FlashGoogleGemini 3 Flash PreviewGoogleGrok 4.20 (Reasoning)xAI
Capability
Capabilities Index (ECI)154.5 (best)151.8152.0
ECI rank#33 of 148 (best)#43 of 148#41 of 148
GPQA DiamondGraduate-level science questions92.8% (best)89.4%89.3%
FrontierMath Tiers 1–3Research-level mathematics62.8% (best)51.2%44.9%
OTIS Mock AIME 2024–2025Competition mathematics95.6% (best)95.6% (best)92.2%
SWE-bench VerifiedFixing real GitHub issues79.3% (best)75.4%—
SimpleQA VerifiedShort factual questions66.2%66.8% (best)30.2%
Price per million tokens
Input$1.50$0.50 (best)$1.25
Output$9.00$3.00$2.50 (best)
Cached input$0.15$0.05 (best)$0.20
Blended (3:1)$3.38$1.13 (best)$1.56
Long-context rateSame rateSame rateOver 200K: $2.50 / $5.00
Price sourceOfficial Google APIOfficial Google APIOfficial xAI API
Limits
Context window1,048,576 tokens (best)1,048,576 tokens (best)1,000,000 tokens
Max output65,536 tokens (best)65,536 tokens (best)30,000 tokens
Inputs and features
TextYesYesYes
ImagesYesYesYes
PDFsYesYesYes
AudioYesYesNo
VideoYesYesNo
ReasoningYesminimal · low · medium · highYesminimal · low · medium · highYes
Tool callingYesYesYes
Structured outputYesYesYes
Availability
WeightsProprietaryProprietaryProprietary
API model IDgemini-3.5-flashgemini-3-flash-previewgrok-4.20-0309-reasoning
API providers32 (best)2011
ReleasedMay 19, 2026Dec 17, 2025Mar 9, 2026
Knowledge cutoffJan 2025Jan 2025—
03 — Cost

What would a month cost?

Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.

  • Gemini 3.5 Flash$33.00
  • Gemini 3 Flash Preview$11.00
  • Grok 4.20 (Reasoning)$17.50
04 — Questions

Which should you choose?

Which is better: Gemini 3.5 Flash, Gemini 3 Flash Preview or Grok 4.20 (Reasoning)?

Gemini 3 Flash Preview is the better all-round choice, scoring 73/100 against Gemini 3.5 Flash (69) and Grok 4.20 (Reasoning) (68). It leads on price. Gemini 3.5 Flash wins on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

Which is cheaper, Gemini 3.5 Flash, Gemini 3 Flash Preview 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); Gemini 3.5 Flash costs $1.50 input / $9.00 output per million tokens (official Google API price). 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 $3.38 for Gemini 3.5 Flash (3× as much).

Which scores higher on benchmarks?

Gemini 3.5 Flash scores higher on the Capabilities Index (ECI): Gemini 3.5 Flash 154.5 (#33 of 148), Grok 4.20 (Reasoning) 152.0 (#41 of 148) and Gemini 3 Flash Preview 151.8 (#43 of 148). The confidence ranges of the top two overlap (152.5–156.6 vs 149.3–154.4), so treat the gap as small. On individual benchmarks: GPQA Diamond — Gemini 3.5 Flash 92.8%, Gemini 3 Flash Preview 89.4%, Grok 4.20 (Reasoning) 89.3%; FrontierMath Tiers 1–3 — Gemini 3.5 Flash 62.8%, Gemini 3 Flash Preview 51.2%, Grok 4.20 (Reasoning) 44.9%; OTIS Mock AIME 2024–2025 — Gemini 3.5 Flash 95.6%, Gemini 3 Flash Preview 95.6%, Grok 4.20 (Reasoning) 92.2%; SimpleQA Verified — Gemini 3 Flash Preview 66.8%, Gemini 3.5 Flash 66.2%, Grok 4.20 (Reasoning) 30.2%.

Which is better for coding?

There are no published SWE-bench Verified results for Grok 4.20 (Reasoning) yet, so there is no like-for-like coding score. On overall capability, Gemini 3.5 Flash 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 3.5 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 3.5 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 3.5 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 3.5 Flash handles the widest range of inputs.

Are any of these open source?

No. Gemini 3.5 Flash, Gemini 3 Flash Preview and Grok 4.20 (Reasoning) are proprietary and only available through APIs and apps.

Which is newer?

Gemini 3.5 Flash is the newest, released May 19, 2026. Grok 4.20 (Reasoning) came out Mar 9, 2026; Gemini 3 Flash Preview came out Dec 17, 2025. Knowledge cutoff: Gemini 3.5 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.

05 — Keep comparing

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