Type Alias: TaggedCustomEvent<T>#

type TaggedCustomEvent<T = unknown> =
  | StructuredOutputStartEvent
  | StructuredOutputCompleteEvent<T>
  | ApprovalRequestedEvent
  | ToolInputAvailableEvent;

Defined in: packages/typescript/ai/src/types.ts

Discriminated union of the orchestrator-tagged CUSTOM events. Each variant has a literal name, so a single narrow on chunk.name yields a typed value with no helper or cast:

if (chunk.type === 'CUSTOM' && chunk.name === 'approval-requested') {
  chunk.value.toolCallId // typed as string
}

The StructuredOutputCompleteEvent value is parameterized by T, which the chat orchestrator narrows to the schema's inferred type after Standard Schema validation. Adapters always emit it with T = unknown.

TaggedCustomEvent is included in TypedStreamChunk's typed-tools branch so consumers iterating chat() streams get tagged narrowing alongside the per-tool TOOL_CALL_START/TOOL_CALL_END typing.

Caveat: user-emitted custom events#

Tools can emit arbitrary user-defined custom events via the emitCustomEvent(name, value) context API. Those flow through the stream at runtime but are intentionally absent from this union — including a bare CustomEvent (whose value: any would poison the union) would collapse chunk.value back to any after the narrow. If you rely on emitCustomEvent, branch on CUSTOM outside the literal-name narrows or cast the chunk to StreamChunk to recover the wider shape.