# Kimi K3 API: how to get a key and make your first call

By SeedRouter · Published 2026-09-28 · Updated 2026-09-28

To call Kimi K3, you need an API key from a platform that serves it and a request with `model` set to `kimi-k3`. Moonshot AI serves it on its own [Kimi API Platform](https://platform.kimi.ai/docs/guide/kimi-k3-quickstart), where the model unlocks after a first top-up. SeedRouter serves it with one key, pay-as-you-go, in the official request format: point the OpenAI SDK at `https://api.seedrouter.ai/v1` and keep your code.

This guide uses SeedRouter; the request bodies are the same as Kimi's own API.

## How do I get a Kimi K3 API key?

1. Sign in to SeedRouter and open **API keys**.
2. Create a key and copy it; it is shown once.
3. Add credit when you need it. New accounts start with a small free balance, and there is no subscription.

Keep the key in an environment variable such as `SEEDROUTER_API_KEY`, and only use it from server-side code.

## How do I call Kimi K3 from Python?

Kimi K3 speaks the Chat Completions format, so the official `openai` package works as is:

```python
import os
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["SEEDROUTER_API_KEY"],
    base_url="https://api.seedrouter.ai/v1",
)

completion = client.chat.completions.create(
    model="kimi-k3",
    messages=[{"role": "user", "content": "Explain context caching in one sentence."}],
)
print(completion.choices[0].message.content)
```

The answer is in `content`. Kimi K3 reasons before it answers, and that reasoning comes back in `reasoning_content` on the same message.

## How do I call it from Node.js or cURL?

```javascript
import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.SEEDROUTER_API_KEY,
  baseURL: "https://api.seedrouter.ai/v1",
});

const completion = await client.chat.completions.create({
  model: "kimi-k3",
  messages: [{ role: "user", content: "Explain context caching in one sentence." }],
});
console.log(completion.choices[0].message.content);
```

```bash
curl https://api.seedrouter.ai/v1/chat/completions \
  -H "Authorization: Bearer $SEEDROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "kimi-k3", "messages": [{"role": "user", "content": "Explain context caching in one sentence."}]}'
```

The same key also answers the Responses API (`/v1/responses`) and the Anthropic Messages format (`/v1/messages`) for `kimi-k3`.

## How do I set reasoning effort?

Kimi K3 always reasons; you cannot turn it off. `reasoning_effort` sets how much it thinks before answering:

```python
completion = client.chat.completions.create(
    model="kimi-k3",
    messages=[{"role": "user", "content": "Find the bug: def avg(xs): return sum(xs) / len(xs)"}],
    reasoning_effort="high",
)
```

| Value           | Use it for               |
| --------------- | ------------------------ |
| `low`           | Quick, simple steps      |
| `high`          | Most coding and analysis |
| `max` (default) | The hardest problems     |

Reasoning tokens are billed as output and count toward `max_completion_tokens`, which defaults to 131,072 and goes up to 1,048,576. In our test on the same question, `low` used 25 output tokens and `max` used 146.

## How do I stream the answer?

Add `stream=True`. Reasoning arrives first in `delta.reasoning_content`, then the answer in `delta.content`. Ask for `stream_options={"include_usage": True}` to get the token counts in the last chunk:

```python
stream = client.chat.completions.create(
    model="kimi-k3",
    messages=[{"role": "user", "content": "Write a haiku about latency."}],
    stream=True,
    stream_options={"include_usage": True},
)
for chunk in stream:
    if chunk.choices and chunk.choices[0].delta.content:
        print(chunk.choices[0].delta.content, end="", flush=True)
```

## Can I send images?

Yes, as base64 data URIs. Kimi K3 does not accept public image URLs; its [quickstart](https://platform.kimi.ai/docs/guide/kimi-k3-quickstart) says "Vision input does not support public image URLs":

```python
import base64

with open("chart.png", "rb") as f:
    image = base64.b64encode(f.read()).decode()

completion = client.chat.completions.create(
    model="kimi-k3",
    messages=[{
        "role": "user",
        "content": [
            {"type": "image_url", "image_url": {"url": f"data:image/png;base64,{image}"}},
            {"type": "text", "text": "What does this chart show?"},
        ],
    }],
)
```

## What errors should I expect?

| Error                                           | Cause                                     | Fix                              |
| ----------------------------------------------- | ----------------------------------------- | -------------------------------- |
| 400 on `temperature`, `top_p`, `n` or a penalty | Kimi K3 fixes them (1.0, 0.95, 1, 0)      | Leave them out                   |
| 400 on `reasoning_effort`                       | A value other than `low`, `high` or `max` | Use one of the three             |
| 400 on an image                                 | A public URL instead of a data URI        | Send the image as base64         |
| 401                                             | Missing or wrong key                      | Check the `Authorization` header |

Errors return `{"error": {"code": ..., "message": "..."}}`, and a request that fails is not charged.

## Frequently asked questions

### Is the Kimi K3 API OpenAI-compatible?

Yes. Kimi K3 takes the Chat Completions and Responses formats, so the OpenAI SDK works with only the base URL and model changed. It also takes the Anthropic Messages format.

### Do I need a Moonshot account to use Kimi K3?

Not on SeedRouter. You sign in to SeedRouter, create a key there and pay from your SeedRouter balance.

### How much does a Kimi K3 request cost?

It is billed per input and output token. The [Kimi K3 pricing guide](https://seedrouter.ai/blog/kimi-k3-api-pricing) has the live rates and worked examples.

### Where is the full parameter list?

The [Kimi K3 API reference](https://seedrouter.ai/docs/kimi-k3) lists every field, with the [Kimi K3 page](https://seedrouter.ai/models/kimi-k3) for a playground and live prices.