Reasoning Control

For models that support reasoning (chain-of-thought), you can control the depth of reasoning with the reasoning_effort parameter.

What you’ll learn:

Which models support reasoning control
How to use the reasoning_effort parameter
How to disable reasoning for Qwen3 models

Supported Models

Model	Reasoning Control
o1, o1-mini, o3, o3-mini, o4-mini	`reasoning_effort` parameter
Gemini 2.5	`reasoning_effort` parameter
Claude 3.7, Claude 4	`reasoning_effort` parameter
Qwen3	`/no_think` prompt keyword

Using reasoning_effort

Python

from openai import OpenAI

client = OpenAI()

response = client.chat.completions.create(
    model="claude-sonnet-4",
    messages=[
        {"role": "system", "content": "You are a concise and helpful assistant."},
        {"role": "user", "content": "What is the capital of France?"},
    ],
    reasoning_effort="low",  # "low", "medium", or "high"
)

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

The reasoning_effort parameter accepts three values:

low — Fast responses, minimal reasoning
medium — Balanced reasoning depth
high — Deep reasoning for complex problems

Disabling Reasoning for Qwen3

For Qwen3 models, prepend /no_think to your prompt to disable reasoning:

from openai import OpenAI

client = OpenAI()

response = client.chat.completions.create(
    model="Qwen3-30B-A3B-FP8",
    messages=[
        {"role": "system", "content": "You are a helpful assistant."},
        {"role": "user", "content": "/no_think What is your name?"},
    ],
)

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

Next Steps

Chat Completions — Standard chat API usage
Function Calling — Connect reasoning models to external tools
Streaming — Stream reasoning model responses