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

# LLM

> Voice agents use LLMs (large language models) that understand the conversation context and respond to the user.

By default an agent runs on the Brosbots-managed LLM - this requires no
configuration.

## Managed tiers

On the **Brosbots (managed)** provider you pick a tier, not a concrete model -
the same way you do for [transcription](/en/configurations/transcriber):

| Tier | Model behind it | When |
| - | - | - |
| **Fast** | Gemini 2.5 Flash | What an agent created from a template starts on. The shortest time to the first word: qualifying, routing, confirming a slot, most phone calls. |
| **Smart** | GPT-4o mini | A sensible trade-off between pace, price and following instructions. |
| **Accurate** | GPT-4.1 | Long prompts, branching scripts, tool calls and hard rules the agent must not talk its way around. |

The tier is set in the agent editor, on the **Role** tab. The cost per minute
depends on it and is shown in the estimate next to the configuration. The
estimate uses the same provider rates as billing and assumes the top of the
range: four model requests a minute, each with the full prompt, and an agent
speaking for the whole minute.

The model is usually the largest part of the pause before the agent answers.
If an agent feels sluggish, start with the **Fast** tier and only then touch
[turn detection](/en/configurations/turn-detection). Move to **Accurate**
when the agent loses its instructions on a faster tier.

From the **Pro** plan up you can use your own provider accounts (OpenAI,
Google, Groq): add a key in **Account → Provider keys**, then pick the
provider and model in the agent configuration.

## When the model does not answer

A single model failure (a 5xx, a rate limit, a dropped stream) no longer
means silence on the line:

1. A request that failed, or produced neither a word nor a tool call within
   **10 s**, is sent once more.
2. When that fails too, a fallback tier on **another provider** answers:
   Fast (Gemini) stands in for Smart and Accurate (OpenAI), Smart stands in
   for Fast. For the next 60 s the call starts with the fallback, so every
   turn does not wait for two failures first.
3. When nothing works, the agent says a short apology ("I'm sorry, we're
   having a technical problem...") and ends the call with the
   `service_failure` disposition.

A reply that has already started being spoken, or has called a tool, is not
repeated - a retry would say the same words twice or book the appointment
twice.

Set the fallback with `workflow_configurations.llm_fallback_tier` (`fast`,
`smart`, `accurate` or `none`). An agent on its own provider key has no
fallback until you set one - the fallback runs on the Brosbots key.


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