Reasoning Effort

Kimi K3 always reasons and configures reasoning effort with the top-level reasoning_effort request field. It supports "low", "high", and "max", with "max" as the default.

Set the reasoning effort

Set reasoning_effort at the top level of the Chat Completions request:

{
  "model": "kimi-k3",
  "messages": [{"role": "user", "content": "Derive the general formula for this sequence: 1, 4, 9, 25, 64, ..."}],
  "reasoning_effort": "high"
}

When migrating from K2.x to K3, remove the K2.x thinking configuration and use top-level reasoning_effort as needed.

curl
python

$ curl https://api.moonshot.ai/v1/chat/completions \
    -H "Content-Type: application/json" \
    -H "Authorization: Bearer $MOONSHOT_API_KEY" \
    -d '{
        "model": "kimi-k3",
        "messages": [
            {
                "role": "user",
                "content": "Derive the general formula for this sequence: 1, 4, 9, 25, 64, ..."
            }
        ],
        "reasoning_effort": "high"
    }'

import os
from openai import OpenAI

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

completion = client.chat.completions.create(
    model="kimi-k3",
    messages=[
        {"role": "user", "content": "Derive the general formula for this sequence: 1, 4, 9, 25, 64, ..."},
    ],
    reasoning_effort="high",
)

message = completion.choices[0].message
if hasattr(message, "reasoning_content"):
    print(getattr(message, "reasoning_content"))
print(message.content)

Fields

Field	Type	Required	Description
`reasoning_effort`	string	No	K3’s top-level reasoning-effort field; supports `"low"`, `"high"`, and `"max"`, with `"max"` as the default.

For multi-turn conversations and tool calls, K3 requires the complete assistant message returned by the API to be passed back to messages as-is, including reasoning_content and tool_calls.

Kimi K3 API Tool Calling Best Practices: reasoning-effort configuration guidance for tool-calling scenarios
Thinking Mode: per-model thinking behavior and Preserved Thinking
Model Parameter Reference: parameter differences across models

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Set the reasoning effort

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Set the reasoning effort

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