> ## Documentation Index
> Fetch the complete documentation index at: https://docs.braintrust.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Temperature parameter not supported in GPT-5 models

> [!NOTE]
>
> **Applies to:**
>
> * Plan - Any
> * Deployment - Braintrust-hosted
> *
> * Use case - Prompts using GPT-5 models

## Summary

**Issue:** The `temperature` parameter appears disabled or has no effect when using GPT-5 models in Braintrust prompts.

**Cause:** Whether GPT-5 models accept the `temperature` parameter depends on the reasoning effort. GPT-5.1 and later support `temperature` only when reasoning effort is set to `none`. At any higher reasoning effort, and for older GPT-5 models (`gpt-5`, `gpt-5-mini`, `gpt-5-nano`) and GPT-5 Pro, the API doesn't accept `temperature`, so Braintrust removes it.

**Resolution:** To use `temperature` with a GPT-5 model, select GPT-5.1 or later and set **Reasoning effort** to `none`. If you need both a higher reasoning effort and temperature control, switch to a model that supports `temperature` at any reasoning effort.

## Resolution steps

### Use temperature with a GPT-5 model

#### Step 1: Select GPT-5.1 or later

In the prompt editor, choose GPT-5.1 or a later GPT-5 model. Older GPT-5 models and GPT-5 Pro don't expose a `none` reasoning effort, so they never accept `temperature`.

#### Step 2: Set reasoning effort to none

In the model parameters, set **Reasoning effort** to `none`. The `temperature` parameter is available only at this setting. Raising the reasoning effort removes the `temperature` setting.

#### Step 3: Configure the temperature value

Set your desired temperature value (0.0 to 2.0) in the model parameters.

### If you need a higher reasoning effort and temperature control

#### Step 1: Switch to a compatible model

Change your prompt to a model that supports `temperature` at any reasoning effort, such as GPT-4.1.

#### Step 2: Configure the temperature value

Set your desired temperature value in the model parameters.

## Additional information

This reflects OpenAI's parameter support for each model, not a Braintrust limitation. Refer to OpenAI's model documentation for complete parameter support details for each model family.


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.