Kimi K3 API Guide: Three Steps for Developers After the Subscription Pause

Kimi K3 is everywhere this week — but Moonshot suddenly paused new membership subscriptions, catching developers off guard.

The good news: the API channel remains open. K3’s capabilities are callable directly from the open platform, and they even plug into coding agents like Claude Code. The gap between “clicking a button in an app” and “calling the API from a script,” however, hides a few potholes worth knowing in advance. This guide walks the full path — API key setup, direct-call code, Claude Code configuration — with field-tested pitfalls included. One framing note before the mechanics: K3 is unusually sensitive to how you call it, so most of what follows is less about plumbing and more about the settings that decide whether a request succeeds at all.

Step 1: Get an API Key and Watch the Tier Threshold

Visit the Kimi Open Platform and register or log in.
Create a new key on the “API Keys” page.
Critical threshold: accounts in the free tier (lifetime top-up under 50 yuan) get routed to a low-priority queue — in testing, requests repeatedly returned engine_overloaded_error.
Top up past 50 yuan to auto-promote to Tier-1, where minimal requests start returning HTTP 200 normally.

On pricing: K3 bills by usage; check the official docs for current rates. Note that API credit and subscription quota are separate ledgers — one does not touch the other.

Step 2: Direct API Calls (With Code)

Direct connection is the shortest path. Here is a complete Node.js script that base64-encodes a reference image, sends it to K3, and asks for a single-file webpage:

const fs = require('fs');
const path = require('path');

// 1. Read and encode the image
const imagePath = path.join(__dirname, 'reference.png');
const imageBuffer = fs.readFileSync(imagePath);
const base64Image = imageBuffer.toString('base64');
const mimeType = 'image/png';

// 2. Build the request body
const payload = {
  model: 'kimi-k3',  // K3 model ID
  messages: [
    {
      role: 'user',
      content: [
        {
          type: 'image_url',
          image_url: {
            url: `data:${mimeType};base64,${base64Image}`,
          },
        },
        {
          type: 'text',
          text: 'Analyze this webpage screenshot and generate a fully functional single-file HTML page. Include complete HTML, CSS, and JavaScript. Follow the reference image visual style. Use inline <style> for CSS and inline <script> for JavaScript. The page must open directly in a browser.',
        },
      ],
    },
  ],
  stream: false,  // non-streaming, one-shot return
  max_tokens: 16384,
};

// 3. Send the request
const response = await fetch('https://api.moonshot.cn/v1/chat/completions', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${process.env.KIMI_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify(payload),
});

const data = await response.json();

// 4. Extract the HTML and write it to a file
const htmlContent = data.choices[0].message.content;
const match = htmlContent.match(/```html\n?([\s\S]*?)```/);
const cleanHtml = match ? match[1].trim() : htmlContent;

fs.writeFileSync('output.html', cleanHtml, 'utf-8');
console.log('Page generated: output.html');

Things to know:

Non-streaming mode gives no intermediate feedback — the terminal sits silent for tens of seconds to minutes.
For streaming (stream: true), you must parse SSE data chunk by chunk.
Set a sensible max_tokens — output that is too short gets truncated.
On engine_overloaded_error → check your tier level, or retry later.

Step 3: Plug Into Claude Code (Anthropic-Compatible Endpoint)

If you prefer Claude Code’s agent workflow — file reads and writes, terminal execution, tool calls — you can hang K3 off it:

Configuration

Claude Code switches API endpoints through environment variables:

# In ~/.zshrc or a project .env
export ANTHROPIC_BASE_URL="https://api.moonshot.cn/v1"
export ANTHROPIC_API_KEY="your-kimi-api-key"

Then specify the compatible model ID in Claude Code’s model selector, and requests route to Kimi’s K3 endpoint.

Field findings:

Inside Claude Code, K3 gains agent abilities — file I/O, terminal execution, and so on.
On first generation, the model “thought” without actually writing files to disk → explicitly ask it to check the directory and write.
Visual style drifted — the Claude Code build’s page came out tinted warm red.
The same model behaves noticeably differently inside different agent harnesses.

Pitfall Summary

Every row in this table cost someone real debugging time during the first days of access, so it is worth reading twice before your first serious run. Notice how many of the failures look like service problems but are actually account-tier or interaction-design problems — the platform rarely tells you which one you are hitting.

Problem	Symptom	Fix
Insufficient balance	engine_overloaded_error	Top up ≥50 yuan to reach Tier-1
No feedback in non-streaming mode	Terminal silent for a long time	Switch to streaming or add a timeout
Agent doesn't write files	Seems finished but no file appears	Add "check the directory and confirm the file was written"
API compatibility	Intermediate proxy layer returns 502	Connect directly; minimize proxy layers
Fast token burn	One prompt eats a lot of quota	Shorten the prompt, reduce output length

Practical Advice

Everything above reduces to one routing rule: match the interface to the task’s iteration needs. A one-shot generation with a clear spec is a direct API call; anything requiring judgment, revision, or tool use belongs in an agent shell where the model can see its own outputs and correct them. Budget planning follows the same logic — estimate tokens per run at your expected output length, multiply by your real call volume, and keep a buffer, because K3’s pricing rewards shorter, better-specified prompts rather than long exploratory ones.

Simple tasks: go direct. For standalone jobs (image → HTML), the plain API beats an agent on both speed and stability.
Complex tasks: use the agent. Multi-round iteration, file operations, and command execution are where Claude Code’s loop shines.
Don’t trust model names alone. The same K3 behaves visibly differently across harnesses — choosing the shell matters as much as choosing the model.
Budget ahead. K3’s token consumption is not light — estimate cost before you call.