It's almost there.

Soon.

This is a list of the longest novels over 500,000 words published through a mainstream publisher.

https://en.wikipedia.org/wiki/List_of_longest_novels

And if you check the story stats, The Chase is currently only the second longest story on FiMfiction. I'd wager you're going to take the top slot eventually, Kudzu. I know you've still got a fair bit to go yet.

4552489
And for some reason, I feel like that 'soon' should be presented more ominously.

Um, the stats are bugged. Look at the actual longest story page. The Chase is number one.

It is the longest story that has been published in one part on fimfiction.
http://www.fimfiction.net/user/BlackRoseRaven 's 'Blooming moon' is reasonably arguably longer - only considering the luna-focussed bits.

Then there is http://www.fimfiction.net/user/Imploding+Colon 's http://www.fimfiction.net/story/25966/austraeoh - which involves a fair amount of flying east.

It is rapidly approaching even the sum of all of the parts of either of these though.

Outside of FIM - http://storiesonline.net/s/50474/arlene-and-jeff (nsfw) I think may edge it out for the moment.

Also - dear god - https://www.fanfiction.net/s/4112682/1/The-Subspace-Emissary-s-Worlds-Conquest 4 million words.