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

# Model Selector

> Choose which AI model you want to power Julius, and understand when to use each option.

## Overview

Julius lets you choose which AI model powers your analysis. Use the **Model Selector** in the chat dropdown to switch between models depending on your task.

Models are split into two groups: **Julius models** (tuned for data analysis) and **General models** (third-party models from OpenAI and Anthropic).

## Julius models

Julius models are purpose-built for data work. They're the default and the best starting point for most tasks.

| Model                | Available on       | Best for                             |
| -------------------- | ------------------ | ------------------------------------ |
| **Julius 1.2 Lite**  | All plans          | Quick questions and simple lookups   |
| **Julius 1.2**       | Paid plans         | Most questions and everyday analysis |
| **Julius 1.2 Max**   | Paid plans         | Complex, multi-step analysis         |
| **Julius 1.2 Ultra** | Max plan and above | The most demanding, multi-step work  |

## General models

You can also use third-party models directly. These are useful when you want a different reasoning style or want to compare outputs.

| Model                 | Available on | Description                      |
| --------------------- | ------------ | -------------------------------- |
| **GPT-5.5**           | Paid plans   | OpenAI's most capable model      |
| **Claude Opus 4.8**   | Paid plans   | Anthropic's most powerful model  |
| **Claude Sonnet 4.6** | Paid plans   | Anthropic's fast, balanced model |

> Plan availability can change. Check your workspace settings for the most current details.

## Code environment

The model selector also includes your **code environment** settings:

* **Sandbox** is the container where Julius runs code. You can reset, delete, or expand resources (RAM/CPU) from here.
* **Code runtime** lets you switch between **Python**, **R**, **Lean Python** (a lighter Python environment), and **GPU**.

For more on containers and resource options, see [Containers](/get-started/containers).

## Choosing the right model

* Start with **Julius 1.2** unless you have a specific reason to switch. It's tuned for data analysis and handles most tasks well.
* Use **Julius 1.2 Max** (or **Julius 1.2 Ultra** on higher plans) for complex prompts that involve multiple steps or large datasets.
* Use **Julius 1.2 Lite** when you need a fast answer to a simple question.
* Try a **General model** for a different reasoning style, or to compare outputs across providers.