PostableMessage

PostableMessage is the union of all message formats accepted by thread.post() and sent.edit().

type PostableMessage = AdapterPostableMessage | AsyncIterable<string | StreamChunk | StreamEvent>;

String

Raw text passed through as-is to the platform.

await thread.post("Hello world");

PostableRaw

Explicit raw text — behaves the same as a plain string.

await thread.post({ raw: "Hello world" });

PostableMarkdown

Markdown converted to each platform's native format.

await thread.post({ markdown: "**Bold** and _italic_" });

PostableAst

mdast AST converted to each platform's native format. See Markdown for builder functions.

import { root, paragraph, text, strong } from "chat";

await thread.post({
  ast: root([paragraph([strong([text("Hello")])])]),
});

PostableCard

Rich card with interactive elements. See Cards for components.

import { Card, Text } from "chat";

await thread.post(Card({ title: "Hello", children: [Text("World")] }));

You can also pass a card with explicit fallback text:

await thread.post({
  card: Card({ title: "Hello", children: [Text("World")] }),
  fallbackText: "Hello — World",
});

AsyncIterable (streaming)

An async iterable of strings, StreamChunk objects, or stream events. The SDK streams the message in real time using platform-native APIs where available.

You can yield structured StreamChunk objects for rich content like task progress cards on platforms that support it (Slack). See Streaming for details.

Both AI SDK stream types are supported:

// fullStream (recommended) — preserves step boundaries in multi-step agents
const result = await agent.stream({ prompt: message.text });
await thread.post(result.fullStream);

// textStream — plain string chunks
await thread.post(result.textStream);

When using fullStream, the SDK auto-detects text-delta and finish-step events, extracting text and inserting paragraph breaks between agent steps.

FileUpload

Used in the files field of any structured message format.