API - Does a thread have new content?

Hello, I'm trying to use the API to determine if a thread has new content for me, since the last time I viewed it. E.g. did someone reply after I viewed a thread last.

I tried comparing total replies and read replies, but this does not work if I haven't viewed all the pages in a thread.

(If I view page 1/3 and page 3/3 of a thread, the API tells me I have unread replies. Technically true, because I didn't view page 2/3, but not helpful in this case.)

Has anyone figured this out?