Reasoning

Reasoning models generate intermediate thinking tokens before their final response. Model families differ in whether reasoning can be disabled, how effort levels behave, and how reasoning is returned.

Model	Default	`reasoning_effort`	Disable reasoning	Availability
`qwen-3.8-27b`	`high`	`none`, `low`, `medium`, `high`	Set `reasoning_effort` to `none`	Public shared tier
`kimi-k2.7-code`	Always enabled	Accepted but ignored	Not supported	Customer trials only
`gpt-oss-120b`	`medium`	`low`, `medium`, `high`	Not supported	Public shared tier
`gemma-4-31b`	Disabled	`none`, `low`, `medium`, `high`	Set `reasoning_effort` to `none`	Dedicated endpoints

Reasoning tokens count toward max_completion_tokens and the completion-token usage reported by the API.

Reasoning format

Use reasoning_format to control how supported models return reasoning.

Format	Behavior
`parsed`	Returns reasoning separately in `choices[0].message.reasoning` or streaming `choices[0].delta.reasoning`
`raw`	Prepends reasoning to the final content when the model supports it
`hidden`	Omits reasoning text while still generating and counting reasoning tokens
`none`	Uses the model’s default response format

Format support is model-specific:

Model	Default response behavior	`raw`	`hidden`
`qwen-3.8-27b`	Reasoning returned separately	Does not change the separated response format	Not supported
`kimi-k2.7-code`	`parsed`	Supported	Not supported
`gpt-oss-120b`	Parsed reasoning	Supported	Supported
`gemma-4-31b`	Reasoning disabled until enabled	Not supported	Not supported

For kimi-k2.7-code, do not combine reasoning_format set to raw with response_format types json_object or json_schema.

Parsed response

from cerebras.cloud.sdk import Cerebras

client = Cerebras()

response = client.chat.completions.create(
    model="qwen-3.8-27b",
    messages=[{"role": "user", "content": "Which is larger, 9.11 or 9.9? Explain."}],
    reasoning_format="parsed",
)

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

For streaming responses, reasoning arrives in choices[0].delta.reasoning and final-answer text arrives in choices[0].delta.content.

Qwen 3.8 27B

qwen-3.8-27b enables reasoning by default at high effort.

Value	Behavior
`none`	Disables reasoning
`low`	Selects Qwen’s low reasoning mode
`medium`	Selects Qwen’s medium reasoning mode
`high`	Selects Qwen’s native `xhigh` mode and is the default

Effort levels select reasoning modes. They do not reserve or guarantee an exact reasoning-token budget.

response = client.chat.completions.create(
    model="qwen-3.8-27b",
    messages=[{"role": "user", "content": "Find the bug in this concurrency design."}],
    reasoning_effort="high",
)

To disable reasoning for a simpler request:

response = client.chat.completions.create(
    model="qwen-3.8-27b",
    messages=[{"role": "user", "content": "Return only the word ready."}],
    reasoning_effort="none",
)

Do not send Qwen-native parameters such as disable_reasoning, enable_thinking, preserve_thinking, or thinking_budget. Use reasoning_effort and clear_thinking instead.

Multi-turn reasoning and `clear_thinking`

Chat Completions is stateless, so your application must resend conversation history. When you include an earlier assistant message with its reasoning field, clear_thinking controls whether Qwen receives that historical reasoning:

Value	Behavior
`false` or omitted	Preserves historical assistant reasoning. This is the default.
`true`	Removes historical assistant reasoning before the model is prompted. Assistant final-answer content remains in the history.

from cerebras.cloud.sdk import Cerebras

client = Cerebras()

messages = [{"role": "user", "content": "Design a retry strategy for this job queue."}]
first = client.chat.completions.create(
    model="qwen-3.8-27b",
    messages=messages,
)

assistant = first.choices[0].message
messages.extend([
    {
        "role": "assistant",
        "content": assistant.content,
        "reasoning": assistant.reasoning,
    },
    {"role": "user", "content": "Now account for duplicate delivery."},
])

# Preserve the earlier reasoning. This is also the default when omitted.
preserved = client.chat.completions.create(
    model="qwen-3.8-27b",
    messages=messages,
    clear_thinking=False,
)

# Use the same visible conversation, but remove earlier reasoning from the prompt.
cleared = client.chat.completions.create(
    model="qwen-3.8-27b",
    messages=messages,
    clear_thinking=True,
)

Kimi K2.7 Code

kimi-k2.7-code is currently available only for customer trials. Reasoning is always enabled. The API accepts reasoning_effort for client compatibility but ignores its value, including none.

response = client.chat.completions.create(
    model="kimi-k2.7-code",
    messages=[{"role": "user", "content": "Review this patch for race conditions."}],
    reasoning_effort="low",  # Accepted, but does not change Kimi's reasoning behavior.
    reasoning_format="parsed",
)

Kimi defaults to parsed reasoning and also supports raw. It does not support hidden. clear_thinking is not implemented and should not be sent.

GPT OSS 120B

Use reasoning_effort to select low, medium, or high. The default is medium.

response = client.chat.completions.create(
    model="gpt-oss-120b",
    messages=[{"role": "user", "content": "Explain quantum entanglement."}],
    reasoning_effort="medium",
)

GPT OSS supports parsed, raw, and hidden reasoning formats. When using raw, reasoning and final content are concatenated without separators.

Gemma 4 31B

Reasoning is disabled by default for gemma-4-31b.

Value	Behavior
`none`	Reasoning disabled and is the default
`low`, `medium`, or `high`	Reasoning enabled. The three active values currently behave equivalently.

Gemma 4 does not support raw, hidden, or clear_thinking.

response = client.chat.completions.create(
    model="gemma-4-31b",
    messages=[{"role": "user", "content": "Solve this step by step."}],
    reasoning_effort="medium",
)

OpenAI client parameters

reasoning_effort is a standard OpenAI client parameter. Pass Cerebras-specific parameters such as reasoning_format and clear_thinking through extra_body. See OpenAI Compatibility.

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Resources

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Reasoning format

Parsed response

Qwen 3.8 27B

Multi-turn reasoning and `clear_thinking`

Kimi K2.7 Code

GPT OSS 120B

Gemma 4 31B

OpenAI client parameters

​Reasoning format

​Parsed response

​Qwen 3.8 27B

​Multi-turn reasoning and clear_thinking

​Kimi K2.7 Code

​GPT OSS 120B

​Gemma 4 31B

​OpenAI client parameters

Reasoning format

Parsed response

Qwen 3.8 27B

Multi-turn reasoning and `clear_thinking`

Kimi K2.7 Code

GPT OSS 120B

Gemma 4 31B

OpenAI client parameters