I've been a Fastmail user for my personal email for several years now, however I still miss labels. Therefore I love seeing this. It is unclear to me how this

I've been a Fastmail user for my personal email for several years now, however I still miss labels. Therefore I love seeing this. It is unclear to me how this works with IMAP clients. Are these labels still exposed as folders over IMAP? If so, I assume messages get duplicated, just as with Gmail, therefore the client will need special hacks to deal with it, just as with Gmail.