Why was animated GIF size reduced from 5MB to 3.5MB?



I have an app that allows users to directly upload animated gifs to twitter via the REST api. Recently I’ve noticed the api has been returning an error for gifs larger than 3.5MB. This is a recent change because before I could do up to 5MB. Why was this changed,? On the twitter website you can upload images over 5MB. Is this a bug? Thanks