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Comparison · 2 models · Updated Oct 4, 2026

GPT-5.3 Codex vs Gemini 3.1 Pro Preview

Gemini 3.1 Pro Preview comes out ahead, 68 to 64 on our weighted score, and it is the cheaper option too.

  1. OpenAI

    GPT-5.3 Codex

    Released Feb 5, 2026

    64/100
    • ECI156.8
    • Price$1.75 / $14.00
    • Context400K
    Full specs Remove GPT-5.3 Codex
  2. Our pick

    Google

    Gemini 3.1 Pro Preview

    Released Feb 19, 2026

    68/100
    • ECI154.8
    • Price$2.00 / $12.00
    • Context1.05M
    Full specs Remove Gemini 3.1 Pro Preview

  3. Add a model

    Make it a three-way comparison.

01 — Verdict

Gemini 3.1 Pro Preview is our pick

Gemini 3.1 Pro Preview is the better all-round choice, scoring 68/100 against GPT-5.3 Codex (64). It leads on inputs & features and context window. GPT-5.3 Codex wins on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityGPT-5.3 CodexCapabilities Index (ECI): GPT-5.3 Codex 156.8 · Gemini 3.1 Pro Preview 154.8
  • Lowest priceGemini 3.1 Pro PreviewGemini 3.1 Pro Preview $4.50 · GPT-5.3 Codex $4.81 per 1M tokens (3:1 blend)
  • Longest contextGemini 3.1 Pro PreviewGemini 3.1 Pro Preview 1,048,576 · GPT-5.3 Codex 400,000 tokens
  • Widest inputsGemini 3.1 Pro PreviewGPT-5.3 Codex: Text, Images, PDFs · Gemini 3.1 Pro Preview: Text, Images, PDFs, Audio, Video
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightGPT-5.3 CodexGemini 3.1 Pro Preview
CapabilityCapabilities Index (ECI)50%8784
Price25%1819
Inputs & features15%80100
Context window10%4461
Overall100%64/10068/100
02 — Side by side

Every spec in one table

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

GPT-5.3 Codex vs Gemini 3.1 Pro Preview specifications side by side
SpecificationGPT-5.3 CodexOpenAIGemini 3.1 Pro PreviewGoogle
Capability
Capabilities Index (ECI)156.8 (best)154.8
ECI rank#18 of 148 (best)#31 of 148
GPQA DiamondGraduate-level science questions—94.4%
FrontierMath Tiers 1–3Research-level mathematics—59.7%
OTIS Mock AIME 2024–2025Competition mathematics—95.6%
SWE-bench VerifiedFixing real GitHub issues74.8%75.6% (best)
SimpleQA VerifiedShort factual questions—73.5%
Price per million tokens
Input$1.75 (best)$2.00
Output$14.00$12.00 (best)
Cached input$0.175 (best)$0.20
Blended (3:1)$4.81$4.50 (best)
Long-context rateSame rateOver 200K: $4.00 / $18.00
Price sourceOfficial OpenAI APIOfficial Google API
Limits
Context window400,000 tokens1,048,576 tokens (best)
Max output128,000 tokens (best)65,536 tokens
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesYes
AudioNoYes
VideoNoYes
ReasoningYeslow · medium · high · xhighYeslow · medium · high
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryProprietary
API model IDgpt-5.3-codexgemini-3.1-pro-preview
API providers1926 (best)
ReleasedFeb 5, 2026Feb 19, 2026
Knowledge cutoffAug 31, 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.

  • GPT-5.3 Codex$45.50
  • Gemini 3.1 Pro Preview$44.00
04 — Questions

Which should you choose?

Which is better: GPT-5.3 Codex or Gemini 3.1 Pro Preview?

Gemini 3.1 Pro Preview is the better all-round choice, scoring 68/100 against GPT-5.3 Codex (64). It leads on inputs & features and context window. GPT-5.3 Codex wins on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

Which is cheaper, GPT-5.3 Codex or Gemini 3.1 Pro Preview?

Gemini 3.1 Pro Preview is cheaper at $2.00 input / $12.00 output per million tokens (official Google API price). GPT-5.3 Codex costs $1.75 input / $14.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $4.50 per million tokens for Gemini 3.1 Pro Preview versus $4.81 for GPT-5.3 Codex (1.1× as much).

Which scores higher on benchmarks?

GPT-5.3 Codex scores higher on the Capabilities Index (ECI): GPT-5.3 Codex 156.8 (#18 of 148) and Gemini 3.1 Pro Preview 154.8 (#31 of 148). The confidence ranges of the top two overlap (153.5–160.8 vs 152.6–157.3), so treat the gap as small. On individual benchmarks: SWE-bench Verified — Gemini 3.1 Pro Preview 75.6%, GPT-5.3 Codex 74.8%.

Which is better for coding?

Gemini 3.1 Pro Preview resolves more real GitHub issues on SWE-bench Verified: Gemini 3.1 Pro Preview 75.6% and GPT-5.3 Codex 74.8%. Both support tool calling for agent workflows.

Which has the bigger context window?

Gemini 3.1 Pro Preview has the largest context window at 1,048,576 tokens, against 400,000 for GPT-5.3 Codex. Maximum output per response: GPT-5.3 Codex up to 128,000, Gemini 3.1 Pro Preview up to 65,536 tokens.

Which can read images, PDFs, audio or video?

GPT-5.3 Codex accepts text, images and PDFs; Gemini 3.1 Pro Preview accepts text, images, PDFs, audio and video. Gemini 3.1 Pro Preview handles the widest range of inputs.

Are any of these open source?

No. GPT-5.3 Codex and Gemini 3.1 Pro Preview are proprietary and only available through APIs and apps.

Which is newer?

Gemini 3.1 Pro Preview is the newest, released Feb 19, 2026. GPT-5.3 Codex came out Feb 5, 2026. Knowledge cutoff: GPT-5.3 Codex Aug 31, 2025, Gemini 3.1 Pro 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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