Kimi K3 の思考プロセス設計の秘密

Kimi K3, Moonshot AI’s latest open-weight1 model, ranks 1st on our single-shot Frontend Arena with an Elo of 1392. This is 10 positions higher than Kimi K2.6 and 16 positions higher than Kimi K2.7 Code, marking the largest jump we’ve seen in the Moonshot model line.

However, we found that Kimi K3 uses an extreme amount of thinking tokens, using over 12x more reasoning than Claude Opus 4.8 and over double that of Kimi K2.6.

This is a *lot* of reasoning, and we decided to dig deeper to find out exactly what Kimi K3 is thinking about.

We find that Kimi K3’s performance can be primarily ascribed to its unique chain-of-thought approach where it appears to iterate upon designs much like how a full AI agent would, but inside its chain of thought. This strategy produces intricate, intentional websites with creative component design, as well as improves Kimi K3's ability to integrate with outside dependencies.

How Kimi K3 Simulates an Agent in its Chain of Thought

A brief scan through Kimi K3’s thinking traces is all we need to explain its performance. Kimi K3 has unique multi-staged thinking traces, where it switches from planning to decision making to designing individual parts of the final website. This is exactly the agentic workflow, and it’s a pattern we’ve never seen before. In fact, during the final design phases, Kimi K3 writes out sample code so that in the final generation, it can correctly create the interactions it had painstakingly designed.

Compare this to the previous models in the model line, which have much shorter reasoning traces and rarely write code. Instead, they just decide on high-level details or sections before diving straight into the final output.

If we aggregate across all the generations from the Kimi models, we find that it writes over 10x as much code during reasoning than any other model in its model line, with more reasoning tokens spent coding than actually reasoning.

No other model has this density of code blocks during reasoning, and it’s because Kimi K3 iterates on individual components during the reasoning, “testing mentally” instead of using the normal tests it would have in an agent loop. This also implies that Kimi K3 is effectively thinking in code, expressing its planned specification in the form of code and concrete constraints rather than vibing up an inexact plan.

No other large model does this sort of high-level planning and low-level iteration during the reasoning stage, as this strategy increases the amount of time spent reasoning instead of working. By choosing this strategy for its reasoning traces, Kimi K3 deliberately produces results that take more tokens but perform better, essentially trading tokens for intelligence. This results in much slower generations with higher preference scores, setting a new Pareto frontier on our Preference vs Speed chart.

Kimi K3’s Thinking Weaponizes Unsplash Images

However, Kimi K3 has a secret weapon: phenomenal indexing on its training data. Ordinarily, reasoning is much weaker than an agentic trace because the agent can’t use tools like web search to update its internal thinking. However, for Kimi K3, its learned index of the Internet is so strong that it can simply check its mental index for if the reasoning it just output was up-to-date and correct. Below is an example of Kimi K3 using this for Unsplash, a free images provider that models commonly use to find hero visuals and other filler images. On top is the chain-of-thought reasoning, and below is the Unsplash CDN image that the model thought about when it generated the ID.

Kimi K3 thinks about what image it wants, one-shots an Unsplash ID for that image, then thinks about whether than Unsplash ID is actually valid to see if it wants to use it.

This means that Kimi K3 is astoundingly good at finding images for its websites. Here’s the website that the above chain-of-thought generated.

Other models, like Fable 5, don’t utilize their learned index as much as Kimi K3 does, nor do they reason as much about the images they generate. Below are some example generation of Kimi K3 versus other models, where Kimi K3 didn’t miss a single image decoration while Claude Fable 5 and Kimi K2.7 Code had to rely on alt text and defaults instead.

This thinking also extends to dependency usage, where Kimi K3 creates better scroll animations, charts, and frontend UIs simply because it’s thinking about how to use those dependencies during reasoning.

What this means for model selection

Kimi K3 is a step forward in design improvements and a huge leap forward for open source models as a whole. Launches like this are a reminder of how fast the open source frontier is moving, and how open source models can present new ideas that push everyone ahead. Every release like this gives researchers and developers more powerful foundations to push from.

We will continue monitoring Kimi K3 performance and how it compares to other models. Congratulations to the Moonshot AI team on the launch, and see if you like Kimi K3 more than other models on DesignArena.ai.

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1Open Weights will release by July 27th, 2026.