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

# Choose a model in MITHUNAI Chat

> Every model in MITHUNAI Chat comes through the Model Gateway: pick one from the Models menu, what auto means, why one may be missing, how usage counts.

You choose a model in MITHUNAI Chat from the model menu at the top of a thread. Every model in that
menu comes through your organisation's [Model Gateway](https://docs.mithunai.com/gateway/overview.md): Chat holds no provider
key of its own, and every message, every tool step and every generated thread title is a Gateway
request, counted against your organisation's Gateway usage and budget.

## Pick a model

1. Open the model menu at the top of the thread. The models are listed under **Models**.
2. Choose one. The next message in this thread uses it.

You can change model part-way through a thread; earlier replies keep the model that wrote them. A new
thread opens on your deployment's **default model**.

Your administrator decides how long the menu is. A deployment with no named model opens on `auto` and
lists everything the Gateway offers. A deployment that names one or more models lists exactly those,
and opens on the first.

## What `auto` means

`auto` is the Gateway's own router: it picks a model and a provider for each request and, if that
provider fails, retries on another. It works from the list each provider key really has: the Gateway
reads that list every six hours, or when an administrator presses **Fetch models**, and remembers for a
day anything the provider refused. A model your account is not entitled to can still be tried first,
so a message can occasionally fail. **If a message fails with "not found" or a refusal from the
provider, send it again or choose a named model you know works**, and ask your administrator to name
it for your deployment. See [Routing and failover](https://docs.mithunai.com/gateway/routing-and-fallbacks.md).

## Why a model is missing

Unless your deployment names its models, the menu lists what the Gateway offers your organisation,
read from the Gateway when Chat loads it. A model is missing when:

* **Your deployment names its models** and this is not one of them. Ask your administrator.
* **No provider for it is set up** in the Gateway. Providers and their keys are added in the Gateway,
  not in Chat.
* **The provider credential behind it is scoped elsewhere.** A credential in the Gateway can be
  limited to a named list of models, and is never used for one outside it.
* **It was added after you opened Chat.** Reload the page.

You cannot paste your own provider key into Chat. That is deliberate: one place holds the keys, and
every token is attributed to your organisation.

## How usage is counted

| What uses the Gateway | Counted |
| - | - |
| Each message you send, and each reply | Yes, on your organisation's Gateway key |
| Each step the model takes with a tool | Yes: a reply that calls the Knowledge tool three times is several requests |
| The title Chat writes for a new thread | Yes, one short request with the thread's model |
| A scheduled chat that runs on its own | Yes, every run |

Separately, each answer the Knowledge tool's `ask_assistant` gives counts against your
organisation's [monthly answers](https://docs.mithunai.com/analyze/usage-and-limits.md), the same allowance as the console, the
widget and the API.

The Gateway's usage and cost figures cover Chat's traffic only: the console, the widget and the API
reach models through the platform directly. They are not the place to read your organisation's total
spend.

## Where your messages go

The text of each turn -- your message, the thread so far, any attached file's text, and what the
Knowledge tool returned -- is sent through the Gateway to the provider of the model you chose, under
that provider's terms. MITHUNAI does not train models on your conversations. See
[Security](https://docs.mithunai.com/security.md).

## Related

* [Model Gateway](https://docs.mithunai.com/gateway/overview.md)
* [Supported models and pricing](https://docs.mithunai.com/gateway/supported-models-and-pricing.md)
* [Virtual keys and budgets](https://docs.mithunai.com/gateway/virtual-keys-and-budgets.md)


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