Kimi K3 API Practical Guide: Pricing, Free Tier and Python Examples

Kimi K3 is the open-weight flagship model released by Moonshot AI. Built on a large-scale Mixture-of-Experts (MoE) architecture with a trillion-scale parameter count, it has quickly become a popular choice for developers who need strong reasoning, stable tool-calling, and genuinely long context windows in Chinese-heavy workloads.

This guide walks you through calling the K3 API in practice: how to get a key, how to wire it up with the standard OpenAI SDK, what the pricing and free tier look like, and where the model fits best.

What Kimi K3 Is Good At

K3 is designed around three strengths:

• Very long context. It ingests long documents natively, which makes it a strong fit for contracts, research reports, and papers without the chunking headaches.
• Reasoning and agents. Tool calling and multi-step planning are stable enough to build automation agents on top of.
• Balanced Chinese and code. It handles Chinese comprehension and generation well while remaining reliable for code tasks.

Because the weights are open, you can self-host K3. But for most teams, calling it through a unified gateway is simpler: no GPU provisioning, no VRAM planning, no autoscaling to babysit.

Why Developers Reach for K3

Getting a Key in 30 Seconds

A unified gateway lets you use one API key to call K3 alongside DeepSeek, GLM, Qwen and others, all behind an OpenAI-compatible interface. The steps are simple:

1. Open the free sign-up page and enter your email.
2. The system issues a key in seconds — no credit card required.
3. The free quota includes 100 requests plus several free-tier models, so you can try K3 immediately.

The gateway base URL is https://yingsuan.top/v1, which is byte-for-byte compatible with the official OpenAI SDK. Migration cost is zero.

Calling K3 with Python

Here is the minimal example using the official openai SDK:

from openai import OpenAI

client = OpenAI(
    api_key="ys_your_unified_key",
    base_url="https://yingsuan.top/v1"
)

resp = client.chat.completions.create(
    model="kimi-k3",
    messages=[
        {"role": "system", "content": "You are a careful technical assistant."},
        {"role": "user", "content": "Explain MoE architecture in three sentences."}
    ],
    temperature=0.6
)

print(resp.choices[0].message.content)

To switch models you only change the model field — for example deepseek-v4-flash. Your application code stays untouched.

Streaming Responses

For chat UIs you usually want token streaming. The same client supports it with one flag:

stream = client.chat.completions.create(
    model="kimi-k3",
    messages=[
        {"role": "user", "content": "Summarize this report in bullet points."}
    ],
    stream=True
)

for chunk in stream:
    delta = chunk.choices[0].delta.content or ""
    print(delta, end="")

Pricing and Free Tier

• Free trial. Sign up and get 100 request credits; several models include a free tier. Try before you pay.
• Pay as you go. Prepaid balance, billed by actual token usage. No monthly fee, no subscription lock-in. Unused balance stays valid and can be refunded.
• Transparent metering. You pay only for what you use, which makes it easy to scale from a small validation flow into production.

Where It Fits

• Summarization and information extraction from long contracts, reports, and papers.
• Multi-step agents and automation workflows.
• Enterprise knowledge-base Q&A and customer-support assistance.
• Code generation and review, often paired with DeepSeek for a cost-effective combo.

FAQ

Is K3 open source?
Yes. K3 is released as open weights, so you can self-host it or call it through a gateway to skip the ops overhead.

K3 or DeepSeek V4?
Prefer K3 for long text and agent workloads. For maximum-cost-efficiency code and reasoning, pair it with the DeepSeek V4-Flash free tier. Holding both behind one gateway gives you the most flexible routing.

Do I need to rewrite a lot of code?
No. The interface is fully OpenAI-compatible; you only swap base_url and api_key.

If you want to try it without standing up your own GPU stack, the gateway mentioned above is a quick place to grab a free key and start calling K3 in minutes.