Chat - Custom message part rendering

Customize selected message parts while preserving the default headless message structure.

Override one or two message part types while keeping the default row layout intact.

Replace only the part types that need branded or domain-specific rendering, and keep the default renderers for everything else.

The demo below uses Message.Content with getDefaultMessagePartRenderer() to override the reasoning part while preserving the default renderers for everything else:

Overriding a part renderer

• Message.Content as the structural message-content surface
• getDefaultMessagePartRenderer() to preserve shipped rendering behavior
• targeted overrides for parts such as reasoning, tool, file, or data-*

Implementation notes

• Keep the override narrow—replace one part type without rebuilding the whole message surface.
• Use a message with multiple part types so the fallback path is visible.
• Keep customization inside Message.Content rather than rebuilding the message from headless primitives.

When to use this pattern

Use this pattern when:

• You like the default message structure.
• Certain message parts need brand-specific rendering.
• You want to preserve most of the default behavior and change only a subset of content.

This pattern fits reasoning disclosures, tool outputs, citations, files, and data-* parts that need richer domain UI than the defaults provide.

Things to watch for

• Use getDefaultMessagePartRenderer() to keep the default renderers for parts you don't override.
• Overriding one part type does not require forking message rows, groups, or the entire message surface.

See also

• See Messages for the default part renderer reference.
• See Slot customization to extend customization beyond message content into row structure.

API

• ChatRoot