Re:A new and improved Twitter API
by jdminhbg on Friday July 17, 2020 @12:07PM
(#23872017)
I'm not sure which hack Tweetbot is using to do this (I think search as noted below), but you can tell it's a hack because it only works for recent-ish tweets. If you go to a tweet a couple weeks old and view details, you can see that it won't fill in the replies.
[ Parent
| on HN ]
Can confirm, Tweetbot never has "all" the replies.
The way clients usually do this is by fetching all mentions to the user after a given timestamp (of the original tweet), and collecting only those that are replies to the tweet. Since there's a limit on how many mentions you can get, you might not get all the replies.
It's been like that at least since 2013.