Reasoning flags are currently only available for the OpenAI GPT OSS model.
To enable reasoning, use the reasoning_effort parameter within the chat.completions.create method. This parameter controls the amount of reasoning the model performs.
1

Initial Setup

Begin by importing the Cerebras SDK and setting up the client.
import os
from cerebras.cloud.sdk import Cerebras

client = Cerebras(
    # This is the default and can be omitted
    api_key=os.environ.get("CEREBRAS_API_KEY"),
)
2

Using Reasoning

Set the reasoning_effort parameter within the chat.completions.create method to enable reasoning capabilities.
stream = client.chat.completions.create(
    messages=[
        {
            "role": "system",
            "content": "You are a helpful assistant."
        },
        {
            "role": "user",
            "content": "Say hello to the world."
        },
        {
            "role": "assistant",
            "content": "Hello, world! 🌍"
        }
    ],
    model="gpt-oss-120b",
    stream=True,
    max_completion_tokens=65536,
    temperature=1,
    top_p=1,
    reasoning_effort="medium"
)

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

​
Reasoning Effort Levels

The reasoning_effort parameter accepts the following values:
  • "none" - No explicit reasoning effort specified (model-dependent default)
  • "low" - Minimal reasoning, faster responses
  • "medium" - Moderate reasoning
  • "high" - Extensive reasoning, more thorough analysis
The default value depends on the specific model being used. For example, "none" will be treated as "medium" for OpenAI models.

​
Response Format

When reasoning is enabled, the response includes a reasoning field containing the model’s internal thought process: 
{
  "id": "chatcmpl-xxx",
  "object": "chat.completion",
  "choices": [
    {
      "message": {
        "role": "assistant",
        "content": "Hello, world!",
        "reasoning": "The user is asking for a simple greeting to the world. This is a straightforward request that doesn't require complex analysis. I should provide a friendly, direct response."
      }
    }
  ]
}