# Why don’t I get billed for the Advanced AI Assistant or Translation add-ons flat fees immediately?

We bill for these add-ons at the end of the billing period so we can include any usage charges alongside the flat fees.

These add-ons will not appear on your bill until they are used for the first time.

The flat fees for these two add-ons include a limited number of actions:

* **Advanced AI Assistant add-on:** includes a set number of successfully answered questions per month, with an additional charge for each answered question beyond that limit.
* **Translations add-on:** includes a set number of translated words per month, with an additional charge per 1000 translated words beyond that limit.

See [our pricing page](https://www.gitbook.com/pricing) for specific limits and pricing for each add-on.