# AssistantRuntime
URL: /docs/api-reference/runtimes/assistant-runtime

Root runtime for managing threads, tool UIs, and assistant state.

The `AssistantRuntime` is the root runtime of the application.

`useAui` \[#useaui]

Access the assistant runtime via `useAui`:

```tsx
import { useAui } from "@assistant-ui/react";

const aui = useAui();

// Thread management
aui.threads().switchToNewThread();
aui.threads().switchToThread(threadId);

// Thread actions
aui.thread().cancelRun();
aui.thread().append(message);
```

<ParametersTable />

Tool UI Registry \[#tool-ui-registry]

The tool UI registry is part of the assistant runtime. It allows you to display custom UI for tool calls, enabling generative UI.