GPT-5.3 Codex vs Kimi K3 vs Gemini 3.1 Pro Preview
Too close to call on our weighted score (Gemini 3.1 Pro Preview 68, Kimi K3 65, GPT-5.3 Codex 64). The right pick depends on what you value most.
OpenAIGPT-5.3 Codex
64/100- ECI156.8
- Price$1.75 / $14.00
- Context400K
Moonshot AIKimi K3
65/100- ECI157.6
- Price$3.00 / $15.00
- Context1.05M
GoogleGemini 3.1 Pro Preview
68/100- ECI154.8
- Price$2.00 / $12.00
- Context1.05M
Too close to call
It is close. Our weighted score puts them within 3 points (Gemini 3.1 Pro Preview 68/100, 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 Gemini 3.1 Pro Preview 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 · 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 · Kimi K3 $6.00 per 1M tokens (3:1 blend)
- Longest contextKimi K3 and Gemini 3.1 Pro PreviewKimi K3 1,048,576 · Gemini 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 · Kimi K3: Text, Images, Video · Gemini 3.1 Pro Preview: Text, Images, PDFs, Audio, Video
- Self-hostingKimi K3Publishes downloadable weights
| Measure | Weight | GPT-5.3 Codex | Kimi K3 | Gemini 3.1 Pro Preview |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 87 | 88 | 84 |
| Price | 25% | 18 | 13 | 19 |
| Inputs & features | 15% | 80 | 80 | 100 |
| Context window | 10% | 44 | 61 | 61 |
| Overall | 100% | 64/100 | 65/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | GPT-5.3 CodexOpenAI | Kimi K3Moonshot AI | Gemini 3.1 Pro PreviewGoogle |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 156.8 | 157.6 (best) | 154.8 |
| ECI rank | #18 of 148 | #13 of 148 (best) | #31 of 148 |
| GPQA DiamondGraduate-level science questions | — | 93.1% | 94.4% (best) |
| FrontierMath Tiers 1–3Research-level mathematics | — | 72.2% (best) | 59.7% |
| OTIS Mock AIME 2024–2025Competition mathematics | — | 97.2% (best) | 95.6% |
| SWE-bench VerifiedFixing real GitHub issues | 74.8% | — | 75.6% (best) |
| SimpleQA VerifiedShort factual questions | — | 50.6% | 73.5% (best) |
| Price per million tokens | |||
| Input | $1.75 (best) | $3.00 | $2.00 |
| Output | $14.00 | $15.00 | $12.00 (best) |
| Cached input | $0.175 (best) | $0.30 | $0.20 |
| Blended (3:1) | $4.81 | $6.00 | $4.50 (best) |
| Long-context rate | Same rate | Same rate | Over 200K: $4.00 / $18.00 |
| Price source | Official OpenAI API | Official Moonshot AI API | Official Google API |
| Limits | |||
| Context window | 400,000 tokens | 1,048,576 tokens (best) | 1,048,576 tokens (best) |
| Max output | 128,000 tokens | 131,072 tokens (best) | 65,536 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | No | Yes |
| Audio | No | No | Yes |
| Video | No | Yes | Yes |
| Reasoning | Yeslow · medium · high · xhigh | Yeslow · high · max | Yeslow · medium · high |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Open | Proprietary |
| API model ID | gpt-5.3-codex | kimi-k3 | gemini-3.1-pro-preview |
| API providers | 19 | 68 (best) | 26 |
| Released | Feb 5, 2026 | Jul 16, 2026 | Feb 19, 2026 |
| Knowledge cutoff | Aug 31, 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.
- GPT-5.3 Codex$45.50
- Kimi K3$60.00
- Gemini 3.1 Pro Preview$44.00
Which should you choose?
Which is better: GPT-5.3 Codex, Kimi K3 or Gemini 3.1 Pro Preview?
It is close. Our weighted score puts them within 3 points (Gemini 3.1 Pro Preview 68/100, 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 Gemini 3.1 Pro Preview on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, GPT-5.3 Codex, Kimi K3 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); 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 $4.50 per million tokens for Gemini 3.1 Pro Preview versus $4.81 for GPT-5.3 Codex (1.1× as much) and $6.00 for Kimi K3 (1.3× as much).
Which scores higher on benchmarks?
Kimi K3 scores higher on the Capabilities Index (ECI): Kimi K3 157.6 (#13 of 148), 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 (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. All three support tool calling for agent workflows.
Which has the bigger context window?
Kimi K3 and Gemini 3.1 Pro Preview have the largest context windows (1,048,576 and 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, 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; Kimi K3 accepts text, images and video; 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?
Kimi K3 publishes its weights and can be self-hosted; GPT-5.3 Codex and Gemini 3.1 Pro Preview is proprietary.
Which is newer?
Kimi K3 is the newest, released Jul 16, 2026. Gemini 3.1 Pro Preview came out 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.
