Android's Gboard always suggests replies in chat apps that fit the context of what my contacts write.

If my previous message had been related, I would assume it predicted what my contact would say in response and make a suggestion based on that. But even if the contact changes the topic, the suggestions are appropriate.

I don't expect that the apps all share the conversation with Gboard. So how are the predictions made.

It seems unlikely that it would take screenshots and base predictions on that. But otherwise I don't know how it is possible.