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

# Latency Optimization

> Minimizing the delay between user speech and agent response

Latency is the "killer" of voice interfaces. A delay of more than 1 second feels unnatural. Butter AI is optimized for sub-second latency, but your configuration choices impact this significantly.

## The Latency Budget

Total Latency = `Network` + `STT` + `LLM` + `TTS` + `Network`

You have control over the **STT**, **LLM**, and **TTS** choices.

## 1. Provider Selection

### STT (Speech to Text)

* **Deepgram Nova-3 / Flux**: Extremely fast and accurate (recommended).
* **ElevenLabs Realtime Scribe v2**: High quality transcription with low latency.
* **Cartesia Ink Whisper**: Optimized for fast conversational turns.
* **AWS Transcribe**: Reliable option for legacy integrations.

### LLM (Language Model)

* **Google Gemini 2.5 Flash Lite**: Optimized for speed and cost-efficiency.
* **Groq (Llama 4 Maverick)**: Ultra-low latency inference for simple tasks.
* **OpenAI GPT-4o**: State-of-the-art balance of intelligence and speed.
* **Anthropic Claude 3.5 Haiku**: Fast and capable reasoning.

### TTS (Text to Speech)

* **Cartesia**: Designed specifically for sub-200ms real-time agents.
* **ElevenLabs Turbo v2**: Best-in-class quality with sub-300ms latency.
* **Amazon Polly Generative**: Consistent performance and quality.

## 2. Server Location

Ensure your SIP trunking and user base are geographically close to the server region you selected when creating your organization. Cross-Atlantic roundtrips add 100ms+ of pure network latency.

## 3. Tool Performance

If your agent calls a custom tool (e.g., `check_inventory`), the agent **cannot speak** until your API responds.

* **Optimize your API**: Ensure your endpoints respond in under 200ms.
* **Async Handoff**: If a task takes long (e.g., 5s), don't make the user wait in silence.
  * *Bad*: (Silence for 5s) -> "Done."
  * *Good*: "I'll check that for you, it might take a moment..." -> (Tool Call) -> "Okay, I found it."

## 4. Prompt Engineering

A long system prompt takes longer to process (input token latency). Keep your prompt focused. Remove unused instructions or examples.