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AI Chat UI Toolkits

Can I ship the same in-app assistant UX on web and React Native (Expo) without rewriting the whole chat runtime?

8 min read

Most teams building in-app assistants for both web and React Native (Expo) hit the same wall: it’s easy to share model logic and tools, but the chat runtime and UX often diverge into two completely different codebases. That usually means duplicated effort, inconsistent experiences, and painful feature rollouts. The good news is you can avoid rewriting everything from scratch—and ship nearly identical assistant UX across web and mobile—if you structure your stack correctly.

This guide explains how to do that, how assistant-ui helps, and what you need to know about sharing a chat runtime between React for web and React Native (Expo).

The core problem: shared agent logic, fragmented UX

Most modern AI stacks already share backend and “brain” layers:

  • The LLM / provider: OpenAI, Anthropic, Groq, etc.
  • Agent logic: built with the Vercel AI SDK, LangChain, LangGraph, or custom code
  • Tools & memory: external APIs, databases, vector search, etc.

The fragmentation happens higher up:

  • Web gets a React chat UI (often custom or using a UI kit)
  • Mobile gets a separate React Native chat UI
  • Streaming, interruptions, retries, and multi-turn logic are implemented twice

Result: every new feature (like a new tool, a different system prompt, or thread persistence) needs to be wired into two runtimes and two UIs. Keeping behavior and UX consistent becomes a constant chore.

What you actually want to reuse

When you say “same in-app assistant UX on web and React Native (Expo) without rewriting the whole chat runtime,” you’re really talking about three layers:

  1. Conversation runtime & state management

    • Streaming responses
    • Handling interruptions / aborts
    • Retries and error states
    • Multi-turn conversations
    • Tool invocation and results
    • Thread persistence and session restore

  2. Interaction model / behaviors

    • How messages are queued and sent
    • How tools are surfaced (slash commands, buttons, mentions)
    • How attachments and structured inputs behave
    • How typing indicators, system messages, and status states are rendered

  3. Visual UX

    • Bubbles, layout, spacing, avatars
    • Theming (dark/light, brand colors)
    • Input area (composer), “send” button, attachments, tool pickers

The trick is to share (1) and (2) across platforms and let (3) adapt per platform as needed.

How assistant-ui helps you avoid two runtimes

assistant-ui is an open-source TypeScript/React library that gives you production-ready AI chat components and state management:

  • Drop-in ChatGPT-style UX with theming and sensible defaults
  • Built-in state management:
    • Streaming
    • Interruptions
    • Retries
    • Multi-turn conversations
  • Works with any LLM provider via:
    • Vercel AI SDK
    • LangChain
    • LangGraph
    • Or your own backend
  • Optionally stores threads in Assistant UI Cloud so sessions persist across refreshes and context builds over time

On web, you can “just install assistant-ui and you’re done” for the chat interface and runtime. The question is: how much of that can you reuse in React Native (Expo)?

Web vs React Native: what’s reusable, what isn’t?

1. Business logic and chat state: reusable

The conversation logic that assistant-ui provides—streaming, message queues, multi-turn, interruptions, retries—sits in a React-friendly state layer, independent of the DOM. This is the part that tends to be portable:

  • Hooks and state machines that manage:
    • messages
    • pending requests
    • tool calls and results
    • error handling
  • Integration with providers through Vercel AI SDK, LangChain, or LangGraph

You can architect your app so that both web and React Native share the same “assistant engine”:

  • Shared TypeScript library (e.g., /packages/assistant-runtime)
  • Web app imports that runtime + assistant-ui’s React components
  • React Native app imports the same runtime and plugs it into RN-native UI components

This means the chat runtime doesn’t need to be rewritten; it only needs platform-specific adapters at the UI layer.

2. UI components: partially reusable

assistant-ui’s pre-built chat components are designed for React web:

  • They assume DOM elements
  • They use CSS/theming specific to web

In React Native (Expo), you can’t render these web components directly. But you can reuse:

  • The data structures (message shapes, tool call shapes)
  • The state hooks / context for threads and streaming
  • The interaction patterns: when to send, how to handle partial tokens, how to cancel, how to retry

You then build a thin layer of RN components (e.g., using <FlatList>, <View>, <TextInput>) that render the same data and behaviors.

This gives you:

  • Same assistant behavior and capabilities
  • Slight differences in platform-specific visual UX, which is actually a good thing (native-feeling vs browser-feeling)

Practical setup: “build once” assistant runtime

Here’s how teams typically structure things to avoid duplicating the chat runtime.

Step 1: Extract a shared “assistant runtime” package

Create a shared package in a monorepo, for example:

/apps
  /web
  /mobile
/packages
  /assistant-runtime
  /api-client

In /packages/assistant-runtime you define:

  • TypeScript models: Message, ToolCall, Thread, etc.
  • Hook(s) to manage chat state, e.g.:
export function useAssistantRuntime(config: AssistantConfig) {
  // Handles:
  // - Messages
  // - Streaming from backend
  // - Interruptions/cancel
  // - Retries
  // - Tool messages
}
  • Provider integrations: Vercel AI SDK, LangChain, LangGraph
  • Thread persistence (e.g., using Assistant UI Cloud or your own store)

This runtime is pure React + TypeScript, no DOM so it works in both React and React Native (Expo).

Step 2: Web: plug runtime into assistant-ui

In your web app:

  1. Import your shared runtime
  2. Wire it into assistant-ui’s production-ready chat components

Example (simplified):

import { AssistantProvider } from '@assistant-ui/react';
import { useAssistantRuntime } from '@myorg/assistant-runtime';

function WebAssistant() {
  const runtime = useAssistantRuntime({ /* config */ });

  return (
    <AssistantProvider runtime={runtime}>
      {/* assistant-ui Chat UI components here */}
    </AssistantProvider>
  );
}

You get:

  • Full ChatGPT-style UX out of the box
  • Streaming, retries, multi-turn, and tools all wired
  • Threads persisted via Assistant UI Cloud if you choose

Step 3: React Native (Expo): plug runtime into native UI

In your Expo app:

  1. Import the same useAssistantRuntime hook
  2. Build a thin set of RN components to render the data:
import { useAssistantRuntime } from '@myorg/assistant-runtime';
import { FlatList, View, TextInput, Button, Text } from 'react-native';

function MobileAssistant() {
  const {
    messages,
    input,
    setInput,
    sendMessage,
    isStreaming,
    retryLastMessage,
    abortStreaming,
  } = useAssistantRuntime({ /* config */ });

  return (
    <View style={{ flex: 1 }}>
      <FlatList
        data={messages}
        renderItem={({ item }) => (
          <Text>{item.role}: {item.content}</Text>
        )}
      />
      {/* Typing indicator based on isStreaming */}
      <View style={{ flexDirection: 'row' }}>
        <TextInput
          value={input}
          onChangeText={setInput}
          placeholder="Send a message..."
          style={{ flex: 1 }}
        />
        <Button title="Send" onPress={sendMessage} />
      </View>
    </View>
  );
}

You’re not rewriting streaming, retries, or tools—you’re just rendering them with native components.

Handling advanced features consistently

assistant-ui is built for production-ready AI chat, not just a basic demo. The more advanced your assistant becomes, the more shared runtime pays off.

Streaming and interruptions

  • Web: assistant-ui’s UI automatically shows streaming tokens and allows interruption
  • Mobile: your RN UI can show a “Stop” button and hook it to abortStreaming
  • Behavior is identical, just rendered differently

Retries and error handling

  • Runtime exposes retryLastMessage or similar utilities
  • Web UI: assistant-ui shows “Retry” buttons inline in the chat
  • Mobile: you render an equivalent retry button in your message bubble component

Tools (functions) and memory

Because assistant-ui is compatible with:

  • LangChain
  • LangGraph
  • Vercel AI SDK

You can centralize:

  • How tools are registered and invoked
  • How tool outputs are formatted as messages
  • How memory/context is managed across turns

Both web and React Native consume the same tool logic; only the presentation differs.

Maintaining a consistent UX across platforms

You likely want the UX to feel “the same” but not necessarily pixel-perfect identical.

Here’s how to align them:

  1. Shared message schema

    • Same role, content, tool_call, metadata structure
    • Ensures features like “tool outputs” or “attachments” show up consistently

  2. Design tokens / theme

    • Base brand colors, spacings, border radius
    • Web: pass theme into assistant-ui
    • Mobile: use the same tokens to style RN components

  3. Interaction patterns

    • Same shortcut patterns where possible:
      • E.g., slash commands, “@tool” mentions
    • Same interpretation of message metadata:
      • System messages, tool messages, error messages, etc.

  4. Platform-specific delights

    • Web: richer hover states, keyboard shortcuts
    • Mobile: gesture-based interactions, native input UX

As long as the runtime and data structures are shared, these platform-specific touches won’t cause behavior drift.

When you still need platform-specific logic

Even with a shared runtime, some things are inherently platform-dependent:

  • File uploads / attachments
    • Web: drag-and-drop, file input
    • Mobile: camera roll, camera, document picker
  • Notifications
    • Web: browser notifications
    • Mobile: push notifications (Expo Notifications)
  • Authentication flows
    • May differ significantly between web and mobile

Handle these via thin platform-specific adapters that connect into the shared runtime’s message and tool layer:

  • Treat attachments as messages or tool invocations
  • Normalize them before they hit the LLM/tooling layer

Answering the core question directly

Yes, you can ship the same in-app assistant UX on web and React Native (Expo) without rewriting the whole chat runtime, as long as you:

  1. Centralize your assistant runtime and state management in a shared TypeScript/React library (streaming, interruptions, retries, multi-turn, tools, memory).
  2. Use assistant-ui on the web to get production-ready ChatGPT-style UX with:
    • Instant chat UI
    • Built-in state management
    • Thread persistence via Assistant UI Cloud (if desired)
  3. Reuse the same runtime in React Native (Expo) and build a thin native UI layer that:
    • Consumes the same hooks/state from your shared runtime
    • Renders messages, streaming, errors, and tools with RN components
  4. Align message schemas, behaviors, and design tokens so the assistant feels consistent across platforms.

You’ll still write some platform-specific UI code for React Native, but you avoid duplicating the chat engine. Streaming, interruptions, retries, multi-turn conversations, and tool handling all live in one place and are shared between web and mobile.

The result: a unified, production-ready assistant experience across web and React Native, with a single source of truth for your chat runtime and AI behavior.

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