AI-assisted disclosure: I used an AI assistant to help structure this write-up. The test runs, timings and logs are my own (kimi.ai free plan, October 28, 2026). Benchmark numbers come from Moonshot's blog and Artificial Analysis, linked at the end.
Short version: one prompt to Kimi K3.1 Pro gave me a playable 3D racing game: a single 752-line HTML file using Three.js, 3 laps, 60 fps, zero page errors. But the file took about 21 minutes to arrive, Kimi's own self-test was still stuck after 38 minutes, and the free plan refused my next prompt 6 times in a row.
▶ Full video: https://youtu.be/iAoYAYFxDQs
What is Kimi K3.1 Pro?
Kimi K3.1 Pro is the new flagship model from Moonshot AI, the Chinese lab behind Kimi. It launched on October 23, 2026.
- Base model: Kimi K3, about 2.8 trillion parameters (mixture of experts)
- Context window: 1 million tokens
- Open weights: Moonshot says the full weights will be released by November 4, 2026
- API price: $2 input / $10 output per million tokens ($0.20 for cached input). A Highspeed variant costs $4 / $20.
Moonshot's headline claim is that it codes almost as well as Claude Opus 5.5. I wanted to see what a normal person gets on the free website.
Test 1: one prompt, one 3D game
This is the exact prompt I sent on kimi.ai (free plan, Kimi K3.1 Pro):
Build a playable 3D racing game in ONE single HTML file using Three.js from a CDN.
Low-poly neon city track at night, the car drives with WASD or arrow keys, chase
camera, 3 laps with a lap timer and best-lap display, a few obstacles to dodge,
and a start screen with "Press Space". No other external assets. Give me the full file.
Kimi came back with "Neon Velocity": one index.html, 752 lines, 47 KB, Three.js loaded from a CDN, a night circuit, nitro, a minimap, lap timers and a finish screen.
To check it honestly, I didn't just eyeball it. I drove it with a script that sends real key presses in headless Chrome on a Mac mini M4:
title screen ready 0.16 s
lap 1 done 19.533 s
lap 2 done 41.033 s
race finished 64.750 s (shown as 1:04.749)
best lap 0:19.516
fps avg 60.5, min 60
page errors 0
draw calls / triangles 36 / 25,554
The only console message was a Three.js warning about the old non-module build. For a single prompt, that is a genuinely good result.
Test 2: speed
This is where it hurt.
- The file was written about 21 minutes after I hit send.
- Kimi then tried to test the game itself in its own browser. It hit a 404 on its own server, switched ports, and its step "Loads game and captures title screen" was still running at 38:53. I stopped it and took the file from the chat.
Artificial Analysis measured the API at about 42.7 tokens per second (No. 184 of 192 models) when I checked, versus about 98 for Claude Opus 5.5.
Test 3: the free plan
Next I asked for a second round: 3 AI rival cars and a race position display. The free plan refused it 6 out of 6 times, including in a brand-new chat and at a lower effort setting:
"Too many people are chatting with Kimi; a subscription will grant you priority access."
So "free" works, but not reliably during busy hours. On the API side it is cheap: Artificial Analysis lists about $3.68 to run its index tasks on Kimi K3.1 Pro versus $10.04 on Opus 5.5.
Test 4: is it really Opus-level?
| Source | Kimi K3.1 Pro | Claude Opus 5.5 |
|---|---|---|
| Moonshot (self-reported): Terminal-Bench 4.0 | 65.7% | 66.4% |
| Moonshot (self-reported): BenchCAD | 92.7% | 96.2% |
| Artificial Analysis: Intelligence Index | 46 (No. 20 of 51) | 58 |
On Moonshot's own chart it's less than a point behind. The independent index puts it well behind, in 20th place. Both can be true: it is very strong at the agentic coding tasks Moonshot picked, and less strong across the board.
The catch
- Slow. 21 minutes for one file, plus a self-test that never finished.
- The free plan gets busy. 6 of 6 follow-up prompts refused.
- "Opus-level" is Moonshot's claim, not the independent ranking.
Verdict
If you want the best coding model today, Claude Opus 5.5 is still smarter and more than twice as fast. But one free prompt built a real, playable 3D game, and the API is about a third of the price. If the open weights really land by November 4, anyone with enough GPUs can run a near-frontier model themselves. That's the part I'll be watching.
Have you tried Kimi K3.1 Pro for coding yet? I'd like to know if you hit the same free-plan wall.
Sources
- Moonshot blog: https://www.kimi.ai/blog/kimi-k3-1-pro
- Kimi API pricing: https://platform.kimi.ai/docs/pricing/chat
- Artificial Analysis: https://artificialanalysis.ai/models/kimi-k3-1-pro
- Moonshot AI on GitHub: https://github.com/MoonshotAI
- Full video: https://youtu.be/iAoYAYFxDQs
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