Transcript.CustomSegment and the .custom case on Transcript.Segment were in the Xcode-beta 27 builds. WWDC26 session 339 covers them as the way a model package extends the protocol for new modalities and server side tool output.
In the Xcode 27 GM they are gone along with the matching action on the executor generation channel.
Is there any additional information as to what happened to custom segments, a replacement, etc? I don't see any mentions of this change in any release notes, though perhaps I'm looking in the wrong place.
Custom segment was replaced by DataEntry and DataAttachment in the latest beta. See the latest details in our documentation.
https://developer.apple.com/documentation/foundationmodels/transcript/dataentry
https://developer.apple.com/documentation/foundationmodels/dataattachmentrepresentable
The TLDR; is that DataEntry is for output produced by the model, and DataAttachmentRepresentable is for things that developers can put inside of prompt builders.
