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

# Model services

> Enable built-in models or configure a custom model provider.

Use **Model services** to manage the models that appear in the chat selector. You can enable Otterflow-provided models or add a compatible custom service.

## Built-in models

Enable an available built-in model on this page, then select it at the top of a chat. Its use counts against your account quota; view the remaining amount and trend in [Account and billing](/en/settings/account-and-billing).

## Custom models

To use your own provider or gateway, add a custom model with the information supplied by that provider:

* model ID;
* API key;
* API endpoint;
* context-window size; and
* API protocol.

Keep credentials private and use the exact endpoint and model name provided by the service.

## Choose a protocol

Use the provider's documented protocol. If you are unsure which option applies, choose **Chat** first. Verify the model with a simple conversation before using it for a larger writing task.

## Tips

* A model must be enabled before it appears in the chat selector.
* Check the configured endpoint, key, and model ID when a custom model cannot be used.
* Changing the available models does not interrupt a reply that is already running.

## See also

* [AI writing](/en/core-features/ai-writing)
* [Account and billing](/en/settings/account-and-billing)