The speedrun for this game ends with the end of act 2, if you haven't gotten that far your good, but even then your probably not going to get much, it obviously skips most of the game.
In any% runs, yeah. But they skip through all the dialogue and cutscenes anyway, so it's barely spoilers. Most of the speedrun is just crazy hops and killing Shadowheart to stuff her corpse in a crate.
AGDQ did an actual all acts speedrun, which does show the actual ending of the game though. And admittedly, more spoilery than a usual run because there's a lot of commentary.