ZMIME
Comparison · 2 models · Updated Oct 4, 2026

GPT-5.3 Codex vs Kimi K3

Too close to call on our weighted score (Kimi K3 65, GPT-5.3 Codex 64). The right pick depends on what you value most.

  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. Moonshot AI

    Kimi K3

    Released Jul 16, 2026

    65/100
    • ECI157.6
    • Price$3.00 / $15.00
    • Context1.05M
    Full specs Remove Kimi K3

  3. Add a model

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01 — Verdict

Too close to call

It is close. Our weighted score puts them within 1 points (Kimi K3 65/100, GPT-5.3 Codex 64/100), so choose by what matters most for your work: Kimi K3 for raw capability and GPT-5.3 Codex on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityKimi K3Capabilities Index (ECI): Kimi K3 157.6 · GPT-5.3 Codex 156.8
  • Lowest priceGPT-5.3 CodexGPT-5.3 Codex $4.81 · Kimi K3 $6.00 per 1M tokens (3:1 blend)
  • Longest contextKimi K3Kimi K3 1,048,576 · GPT-5.3 Codex 400,000 tokens
  • Widest inputsSame inputsGPT-5.3 Codex: Text, Images, PDFs · Kimi K3: Text, Images, Video
  • Self-hostingKimi K3Publishes downloadable weights
How the score is built
MeasureWeightGPT-5.3 CodexKimi K3
CapabilityCapabilities Index (ECI)50%8788
Price25%1813
Inputs & features15%8080
Context window10%4461
Overall100%64/10065/100
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 Kimi K3 specifications side by side
SpecificationGPT-5.3 CodexOpenAIKimi K3Moonshot AI
Capability
Capabilities Index (ECI)156.8157.6 (best)
ECI rank#18 of 148#13 of 148 (best)
GPQA DiamondGraduate-level science questions—93.1%
FrontierMath Tiers 1–3Research-level mathematics—72.2%
OTIS Mock AIME 2024–2025Competition mathematics—97.2%
SWE-bench VerifiedFixing real GitHub issues74.8%—
SimpleQA VerifiedShort factual questions—50.6%
Price per million tokens
Input$1.75 (best)$3.00
Output$14.00 (best)$15.00
Cached input$0.175 (best)$0.30
Blended (3:1)$4.81 (best)$6.00
Long-context rateSame rateSame rate
Price sourceOfficial OpenAI APIOfficial Moonshot AI API
Limits
Context window400,000 tokens1,048,576 tokens (best)
Max output128,000 tokens131,072 tokens (best)
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesNo
AudioNoNo
VideoNoYes
ReasoningYeslow · medium · high · xhighYeslow · high · max
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryOpen
API model IDgpt-5.3-codexkimi-k3
API providers1968 (best)
ReleasedFeb 5, 2026Jul 16, 2026
Knowledge cutoffAug 31, 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
  • Kimi K3$60.00
04 — Questions

Which should you choose?

Which is better: GPT-5.3 Codex or Kimi K3?

It is close. Our weighted score puts them within 1 points (Kimi K3 65/100, GPT-5.3 Codex 64/100), so choose by what matters most for your work: Kimi K3 for raw capability and GPT-5.3 Codex on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

Which is cheaper, GPT-5.3 Codex or Kimi K3?

GPT-5.3 Codex is cheaper at $1.75 input / $14.00 output per million tokens (official OpenAI API price). Kimi K3 costs $3.00 input / $15.00 output per million tokens (official Moonshot AI API price). At a typical mix of three input tokens to one output token, that is $4.81 per million tokens for GPT-5.3 Codex versus $6.00 for Kimi K3 (1.2× as much).

Which scores higher on benchmarks?

Kimi K3 scores higher on the Capabilities Index (ECI): Kimi K3 157.6 (#13 of 148) and GPT-5.3 Codex 156.8 (#18 of 148). The confidence ranges of the top two overlap (154.9–160.4 vs 153.5–160.8), so treat the gap as small.

Which is better for coding?

There are no published SWE-bench Verified results for Kimi K3 yet, so there is no like-for-like coding score. On overall capability, Kimi K3 leads, which tends to carry over to coding, but test on your own codebase. Both support tool calling for agent workflows.

Which has the bigger context window?

Kimi K3 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, Kimi K3 up to 131,072 tokens.

Which can read images, PDFs, audio or video?

GPT-5.3 Codex accepts text, images and PDFs; Kimi K3 accepts text, images and video. They handle the same number of input types.

Are any of these open source?

Kimi K3 publishes its weights and can be self-hosted; GPT-5.3 Codex is proprietary.

Which is newer?

Kimi K3 is the newest, released Jul 16, 2026. GPT-5.3 Codex came out Feb 5, 2026. Knowledge cutoff: GPT-5.3 Codex Aug 31, 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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