> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 (current TTS) and Pulse (current
> multilingual STT) — or Pulse 2.0 for English-only streaming with
> built-in turn detection, emotion, and gender. Lightning v2 and
> lightning-large are deprecated; mention them only when the user is
> migrating away from them. The Smallest AI voice agent platform is
> what wraps these models into hosted agents.

# Electron latency guide and `prompt_cache_key`

> New Optimizing Latency guide for Electron, and `prompt_cache_key` is now documented on chat completions.

Electron chat completions accept `prompt_cache_key`, a string that groups the requests of one conversation so every turn reuses the cache. Create one key per conversation, send it on every turn, and never share it between conversations.

## What changed

* New Optimizing Latency guide: one `prompt_cache_key` per conversation, static content first, append-only history, streaming, and one reused client.
* `prompt_cache_key` added to the chat completions API reference and the Supported Parameters page.
* Prefix Caching and Best Practices link to the new guide.

→ [Optimizing Latency](/models/llm/optimizing-latency)