Currently, OpenAI offers Chat GPT in three main versions: 

Legacy 3.5, Default 3.5, and 4.0. The differences between each version are as follows:

1. Legacy (GPT-3.5) 

The initial model of ChatGPT Plus, it is similar to Turbo mode but slower and generates longer responses.

2. Default (GPT-3.5) 

This version is in Turbo mode, with inference capabilities similar to the Legacy version but faster and generates more concise responses. It is suitable for immediately answering questions that do not require significant logical thinking.

3. GPT-4.0 

This is the most advanced and recent model, available only to Plus paid members. 

It has the highest inference capabilities and generates longer responses, but it is slower.