Model comparison
GPT-5.3-Codex vs Kimi K3
OpenAI against Moonshot AI, compared on context, price, and verified benchmark results.
Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: High — see receipts below
OpenAI
GPT-5.3-Codex
Frontier
Moonshot AI
Kimi K3
Frontier · Open weights
| Specification | GPT-5.3-Codex | Kimi K3 |
|---|---|---|
| Provider | OpenAI | Moonshot AI |
| Tier | Frontier | Frontier |
| Context window | 400K | Winner: 1.05M |
| Max output | 128K | 128K |
| Input / 1M tokens | Winner: $1.75 | $3 |
| Output / 1M tokens | Winner: $14 | $15 |
| Weights | Closed | Open |
| Parameters | Not disclosedUnverified | 2.8T (open-weight MoE) |
| Reasoning levels | none, low, medium, high, xhigh, max | low, high, max |
| Modalities | text, image | text, image, video |
| API model id | gpt-5.3-codex | kimi-k3 |
| Released | February 5, 2026 | July 16, 2026 |
| Artificial Analysis Intelligence Index [high] (2026-08-14) | 52 | Not verifiedUnverified |
| Artificial Analysis Intelligence Index [max] (2026-08-14) | Not verifiedUnverified | 60 |
| Terminal-Bench 2.1 (2026-07-27) | Not verifiedUnverified | 88.3 |
| GPQA Diamond (2026-07-27) | Not verifiedUnverified | 93.5 |
| Humanity's Last Exam (2026-07-27) | Not verifiedUnverified | 56 |
| SWE-bench Verified (2026-09-01) | Not verifiedUnverified | 93.4 |
Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.
Benchmark receipts
- 2026-09-01: vals.ai SWE-bench Verified leaderboard (independent, mini-swe-agent bash-only); not published by Moonshot; a 76.8 aggregator claim is low-reliability — both notedReal GitHub issue resolution: does the model's patch pass the hidden tests. Comparability: comparable with caveat — Post-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.
- 2026-08-14: Artificial AnalysisComposite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).
- 2026-07-27: Kimi K3 HF model card (vendor, with tools; 43.5 no tools)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
Pricing tiers: GPT-5.3-Codex: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Purpose-built for the Codex agent. · Kimi K3: $3/$15 per MTok; cached input $0.30/MTok. Open-weight under the custom Kimi K3 License (not a standard open-source licence). 2.8T MoE with native vision.
GPT-5.3-Codex
GPT-5.3-Codex is OpenAI's coding-specialised model powering the Codex agent at $1.75/$14.
Best for
- Autonomous coding
- Repo-scale refactors
- Test generation
Watch out
Tuned for coding, not general chat; use GPT-5.6 for broad reasoning.
Kimi K3
Kimi K3 is Moonshot AI's open-weight frontier model — 2.8T MoE, 1M context, tied near the top of open-weight leaderboards.
Best for
- Open-weight frontier work
- Long-context
- Multimodal
Watch out
Self-hosting needs large clusters; hosted rates vary.
When the cheaper one wins
GPT-5.3-Codex is cheaper on output at $14 per million tokens against $15 for Kimi K3 — about 1.1×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.
Run the model pickerEvidence confidence: High
How strong and complete the evidence behind this comparison is — not a prediction of which model is better.
- Pricing verified on both sides — Input and output rates are verified for both models.
- 4/5 core specs verified on both sides — Not published for at least one side: parameter count.
- 1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
- Verified within the last 90 days — Newest catalog check was 8 days ago.
- Both models carry source citations — Each side has at least two catalog sources on record.
Source receipts
Each catalog figure was checked against the provider or an independent second source on the date shown.
- GPT-5.3-Codex: OpenAI — Introducing GPT-5.3-Codex (accessed 2026-08-29)
- GPT-5.3-Codex: OpenAI API pricing (gpt-5.3-codex $1.75/$14) (accessed 2026-08-29)
- Kimi K3: HuggingFace — Kimi K3 (accessed 2026-08-29)
- Kimi K3: Moonshot — Kimi K3 guide (accessed 2026-08-29)
Related comparisons
- Claude Fable 5.1 vs GPT-5.3-Codex
- Claude Fable 5.1 vs Kimi K3
- Claude Fable 5 vs GPT-5.3-Codex
- Claude Fable 5 vs Kimi K3
- Claude Mythos 5.1 vs GPT-5.3-Codex
- Claude Mythos 5.1 vs Kimi K3
Diving deeper on one model? GPT-5.3-Codex · Kimi K3
Common questions
GPT-5.3-Codex vs Kimi K3
Answered from the verified figures on this page rather than general guidance.
Is GPT-5.3-Codex or Kimi K3 cheaper for input?
GPT-5.3-Codex is cheaper at $1.75 per million input tokens, against $3 for Kimi K3 — roughly 1.7× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.3-Codex has tiered pricing: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Purpose-built for the Codex agent. Kimi K3 has tiered pricing: $3/$15 per MTok; cached input $0.30/MTok. Open-weight under the custom Kimi K3 License (not a standard open-source licence). 2.8T MoE with native vision.
Is GPT-5.3-Codex or Kimi K3 cheaper for output?
GPT-5.3-Codex is cheaper at $14 per million output tokens, against $15 for Kimi K3 — roughly 1.1× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.3-Codex has tiered pricing: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Purpose-built for the Codex agent. Kimi K3 has tiered pricing: $3/$15 per MTok; cached input $0.30/MTok. Open-weight under the custom Kimi K3 License (not a standard open-source licence). 2.8T MoE with native vision.
Which has the larger context window, GPT-5.3-Codex or Kimi K3?
Kimi K3 accepts 1.05M tokens against 400K for GPT-5.3-Codex. This only matters if you routinely send very long documents or large codebases.
Do GPT-5.3-Codex and Kimi K3 support the same reasoning levels?
GPT-5.3-Codex exposes none, low, medium, high, xhigh, max, while Kimi K3 exposes low, high, max.
Should I use GPT-5.3-Codex or Kimi K3?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. GPT-5.3-Codex suits autonomous coding; Kimi K3 suits open-weight frontier work.
Can I self-host GPT-5.3-Codex or Kimi K3?
Kimi K3 publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. GPT-5.3-Codex is a closed model whose supported access paths are controlled by its provider.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: GPT-5.3-Codex costs $1.75 per 1M tokens versus $3 for Kimi K3 — a 1.7x difference at the headline tier.
- Context: Kimi K3 takes 1.05M against 400K for GPT-5.3-Codex — only decisive if your prompts approach the smaller window.
- Measured capability: Kimi K3 leads Artificial Analysis Intelligence Index 60 to 52 (measured 2026-08-14).
- Deployment: Kimi K3 publishes weights you can self-host; the other is API-only.
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.