Architecture

Kith is structured as a monorepo of six npm packages. The design follows one principle: Kith sits beside your agent, not inside it.

System Diagram

┌──────────────────────────────────────────────────────────────┐
│                        Consumer app                          │
│   (your agent: LangGraph, custom orchestrator, anything)     │
└───────────────┬──────────────────────────────┬───────────────┘
                │                              │
         text (assistant)              subscribe to events
                │                              │
                v                              │
     ┌───────────────────┐        ┌────────────v────────────┐
     │   @kithjs/core    │<───────┤  event bus (KithEvent)  │
     │   contracts only  │        └────────────^────────────┘
     └───────┬───────────┘                     │
             │                                 │
     ┌───────┴───────────────────────────────┐ │
     │                                       │ │
     v                                       v │
┌────────────────┐                ┌──────────┴─────────────┐
│ RuntimeAdapter │                │   VoiceRouter          │
│                │                │   (voice-router)       │
│  ┌──────────┐  │                │   ┌──────────────┐     │
│  │ pipecat  │──┼──> JSON-WS ───┼──>│ ElevenLabs   │     │
│  │ (python  │  │                │   │ Cartesia     │     │
│  │  sidecar)│  │                │   │ OpenAI TTS   │     │
│  └──────────┘  │                │   └──────────────┘     │
│  ┌──────────┐  │                └────────────────────────┘
│  │ livekit  │  │
│  │ (v0.2)   │  │
│  └──────────┘  │
└────────────────┘

Language Boundary

This is a load-bearing decision:

• TypeScript — @kithjs/core and all consumer-facing adapters. Matches the JS ecosystems Kith is built for.
• Python — Pipecat sidecar (spawned as a subprocess). Communicates via JSON over WebSocket.

The extra IPC hop (~20-50ms) buys clean ergonomics for JS-stack consumers without losing Pipecat's pipeline composability.

Adapter Contracts

Adapter	Purpose	v0.1
RuntimeAdapter	Connect, stream text/audio, barge-in, emit events	Pipecat (primary) + LiveKit (stub)
VoiceAdapter	TTS provider routing, pronunciation, chunking	ElevenLabs; Cartesia + OpenAI in v0.2
MemoryAdapter	fetch(turn) -> string[] / save(turn) — pass-through	Interface only; consumer owns storage
ExpressionAdapter	Emits viseme_frame, emotion_state, turn_state	Event emission; no renderer
ObservabilityAdapter	Traces, dup-send guards, reconnect metrics	Fully implemented

Design Principles

1. Stable adapter contracts are the product. The framework's value is that consumers shouldn't care whether the runtime is Pipecat or LiveKit.

2. Events are the contract, not methods. Consumers subscribe to the normalized event bus. Direct method calls on adapters are an implementation detail.

3. Kith sits beside the agent, not inside it. We don't own memory, RAG, tool calling, or persona.

4. Ship the procedural avatar in v0.1. Real VRM + phoneme-to-viseme lipsync is v0.2.