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Overview and router for assistant-ui, the React library for building AI chat interfaces from composable primitives. Use for high-level, cross-cutting, or architecture-overview questions: choosing packages, picking a runtime, or understanding the layered model (RuntimeCore, Runtime, context hooks, primitives) and message model. Covers the `@assistant-ui/react` core plus `@assistant-ui/react-ai-sdk`, `@assistant-ui/react-langgraph`, `assistant-stream`, and `assistant-cloud`; `AssistantRuntimeProvider`; the primitives `ThreadPrimitive`, `MessagePrimitive`, `ComposerPrimitive`; the hooks `useAui`, `useAuiState`, `useAuiEvent`; and runtime selection across `useChatRuntime`, `useExternalStoreRuntime`, `useLangGraphRuntime`, `useLocalRuntime`. For a specific area route to a focused sibling instead: setup, runtime, primitives, tools, streaming, cloud, thread-list, or update. Not for hands-on tasks already owned by those siblings.

Streaming backends and wire protocols for assistant-ui via the assistant-stream package. Use when building a custom (non-AI-SDK) streaming endpoint with createAssistantStreamResponse or createAssistantStreamController, emitting parts through appendText/appendReasoning/appendSource/appendFile/addToolCallPart and setResponse; choosing between the AI SDK Data Stream format (toUIMessageStreamResponse) and the native Assistant Transport format; encoding or decoding streams with DataStreamEncoder/DataStreamDecoder, AssistantTransportEncoder/AssistantTransportDecoder, PlainTextEncoder, or UIMessageStreamDecoder; or wiring streamed chunks into useLocalRuntime or useChatRuntime. Use specifically for debugging stream wire issues: text-delta, part-start, result events, text/event-stream content-type, SSE format, tool calls not rendering, or partial text not showing. For general non-stream debugging route to the relevant focused skill, not the parent overview.

Registers LLM tools and renders custom tool-call UI in assistant-ui (@assistant-ui/react). Use when adding frontend-only tools with makeAssistantTool / useAssistantTool (browser actions like clipboard, navigation, localStorage, async-generator streaming, AbortSignal), rendering backend AI SDK tool() calls with makeAssistantToolUI / useAssistantToolUI (status.type running/complete/incomplete/requires-action, args, result, artifact via ToolCallMessagePartProps), building generative UI from tool results, or implementing human-in-the-loop and approval flows (addResult, resume with context.human(), respondToApproval for server-side needsApproval gates). Covers registering tool components inside AssistantRuntimeProvider and the case-sensitive toolName matching that connects a tool to its UI. Reach for this when tool UI is not rendering, a tool is not being called, or a result is not showing.

Builds and customizes assistant-ui chat UI from composable, unstyled @assistant-ui/react primitives that follow Radix-style part composition. Use when assembling or styling a custom Thread, Composer, message rendering, action bar, or branch picker from building blocks: ThreadPrimitive (.Root, .Viewport, .Messages, .Empty, .ScrollToBottom), ComposerPrimitive (.Input, .Send, .Cancel, .Attachments), MessagePrimitive (.Parts/.Content, .Error), ActionBarPrimitive (.Copy, .Edit, .Reload, .Speak, feedback, .ExportMarkdown), BranchPickerPrimitive, AttachmentPrimitive, ThreadListPrimitive, ThreadListItemPrimitive. Covers MessagePrimitive.Parts children render functions for text, image, reasoning, and tool-call parts; conditional rendering with AuiIf (deprecated .If); and gotchas like wrapping in AssistantRuntimeProvider and adding className since primitives ship unstyled. For prebuilt drop-in UI and scaffolding use setup; for multi-thread sidebar behavior use thread-list.

Guide to the assistant-ui runtime system, single-thread state, and the imperative runtime API in @assistant-ui/react. Use when creating a runtime (useLocalRuntime with a ChatModelAdapter, useExternalStoreRuntime for Redux/Zustand, useRemoteThreadListRuntime), wiring AssistantRuntimeProvider, or reading/mutating thread, message, and composer state and events. Covers the unified hooks useAui, useAuiState, useAuiEvent (composer.send, thread.runStart, thread.runEnd), legacy hooks (useAssistantRuntime, useThreadRuntime, useMessageRuntime, useComposerRuntime, useThread, useThreadMessages), the AssistantRuntime/ThreadRuntime/MessageRuntime/ComposerRuntime hierarchy, thread operations (append, cancelRun, message().edit/reload), capabilities, and types (ThreadMessage, MessagePart, MessageStatus, ChatModelRunResult). Use for provider \"Cannot read property of undefined\" errors or state not updating. For multi-thread list UI and switching between conversations use thread-list instead.

Implements multi-thread (conversation history) management in assistant-ui apps: rendering the prebuilt `ThreadList` next to `Thread`, or building a custom sidebar with `ThreadListPrimitive` and `ThreadListItemPrimitive` (Root, New, Items, Trigger, Title, Archive, Unarchive, Delete). Covers thread CRUD through the `useAui()`/`useAuiState()` API: `switchToThread`, `switchToNewThread`, and per item `rename`, `archive`, `unarchive`, `delete`, `generateTitle`, `initialize`, plus reading `s.threads.threadIds`/`archivedThreadIds`/`mainThreadId`. Includes cloud-backed persistence via `useChatRuntime` + `AssistantCloud` and a local `useRemoteThreadListRuntime` + `InMemoryThreadListAdapter` path. Use when a user wants a thread list/sidebar, switching, searching, sorting, drag-and-drop, or renaming/archiving/deleting conversations. For single-thread state, messages, or composer use runtime; for cloud auth/persistence setup use cloud.