The thinking segment — a collapsible AI reasoning block

Thinking/reasoning segment - collapsible

A segment is data, not an element — it has no tag and dispatches nothing. This one is AparteThinkingSegment, and it is the object you push into a bubble; something else draws it.

Width 375 768 Full Open in a tab

Core's own renderer, drawing the example printed below inside a real viewport. A segment is data — this is what the library makes of it, and it looks the same in every framework.

Example

// No `collapsed` key, so it renders CLOSED — see the field's own note below.
{
  id: 's1',
  type: 'thinking',
  label: 'Reasoning',
  content: 'The question is about transports, so name the two and say where the key lives.',
}

Shape

Discriminated by type: 'thinking'.

Field	Type	Required	Description
content	string	yes
collapsed	boolean	—	Open the block. Absent means CLOSED — a reasoning block is a disclosure, and the reader opens it. More
label	string	—

Shared by every segment

From AparteSegmentBase, which is also what a segment type of your own extends.

Field	Type	Required	Description
id	string	yes	Unique segment identifier
type	string	yes	Segment type discriminator
isStreaming	boolean	—	Whether segment is currently being streamed
messageId	string	—	Id of the message this segment belongs to. Stamped on insertion.
index	number	—	Position in the owning message’s segments[], maintained across insertions and removals.
meta	Record<string, unknown> & { aparte?: AparteSegmentTiming }	—	Extras the producer of the segment knows — token counts, cost, compute device — plus aparte, the one sub-object core writes. More

Notes on individual fields

collapsed

Open the block. Absent means CLOSED — a reasoning block is a disclosure, and the reader opens it.

It used to be the other way round: absent meant open, and core’s own parser emitted collapsed: false on every block it produced, so a reasoning block stayed unfolded for the whole conversation and buried the answer under it. No assistant on the market does that — the content is behind a click, streaming or settled.

false is still how you open one on purpose. Only ABSENT changed meaning.

meta

Extras the producer of the segment knows — token counts, cost, compute device — plus aparte, the one sub-object core writes.

Everything except meta.aparte is yours: fill it with updateSegment(segmentId, { meta }), which MERGES rather than replaces. Mirrors AparteMessage.metadata.

Who emits it

An app pushes one with addSegment() on the viewport, or a parser produces it while a reply streams. Core stamps its identity and timing on insert, so an emitted segment does not have to carry them.

Who draws it

A built-in renderer draws this one, from packages/core/src/renderers/segments/thinking.ts. It installs itself the first time a segment of this type needs it, so a chat renders it with no setup.

Replace it with your own for this config only:

import { registerSegmentRenderer } from '@aparte/core';
import type { AparteThinkingSegment } from '@aparte/core';

registerSegmentRenderer({
    type: 'thinking',
    render: (segment: AparteThinkingSegment) => {
        const el = document.createElement('div');
        el.textContent = JSON.stringify(segment);
        return el;
    },
});

See Customization for the whole renderer seam, and bring your own loop for emitting segments yourself.