What's the longest speedrun world record?

As @Diehe posted, the longest one for a 100% run is definitely this submission for Spider: Rite of the Shrouded Moon with 528h 16m 44s.
(It's worth noting that Snowfats is the only submitter of that category, so I'm not sure to define it a "record".)

Extra: this submission for Baten Kaitos: Eternal Wings and the Lost Ocean with 338h 43m 26s.
(In this case the leaderboard has more than one runner, and it's an actual first place in its category.)

I also tried to find the longest one for Any%:

• This submission for Digimon World 2 with 16h 59m 58s.

• This submission for Xenogears with 19h 41m 49s. (not an official category)

Feel free to point out if I missed something.

There are also a special type of speed run where lower % (less items) takes precedent over time.

Twilight princess has a glitch where it involves looking at a rupee for 17 hours to bypass significant portions of the game

https://www.speedrun.com/tp/run/z5oe0eey

The run is explained here:

Slightly different type of game, but a strong mention for Runescape, specifically old school runescape as it takes longer to max.

A mod tweeted the record for fastest "Maxing" (highest level in each skill) to be ~2136 hours. This is just for one game mode where you can trade other players. For a gamemode "ironman" where you are on your own and cannot trade, the record is ~3400 hours.

This is also just for what we call maxing which is 99 in every skill. You can take this further by getting 200million xp in all skills which is the max amount of xp in a skill. A handful of players have done this now, which is estimated to take about ~15,000 hours.

Source

This equates to:

To put this into hours:
Normal: 2156
Ironman: 3522
Ultimate ironman: 4954
Hardcore ironman: 2863

Key points:

• Normal is the fastest because you can trade and buy supplies to level up with
• In Ironman game modes you play solo, you have to collect everything yourself and you cannot trade other players
• Ultimate ironman is the longest because you have no bank, you have 28 spots in your "bag" and have to use it wisely
• Hardcore ironman means you have 1 life, when you die you return to a normal ironman. Maxing this game mode tends to be faster than maxing a normal ironman because you tend to do less dangerous things such as bossing when you have one life, so you spend more time training and leveling up skills

Honorable mention to this 100% run of Animal Crossing with the added challenge that no Nook codes are used. There's no category for this specific restriction on speedrun.com, but the run itself comes in at 154:40:40 (over several sittings).

The longest one I could find would have to be This run by Snowfats. It is an insane 528h 16m. There is also this one, but it is currently second place in its category.

EDIT: Im not sure what to make of This one...

Race games can be somewhat open-ended, though often have a career mode that includes a large number of races, some of them rather long.

Checking the Gran Turismo series on speedrun.com, GT4 has a 100% speedrun listed at 230h 35m 51 (https://www.speedrun.com/gt4/run/z053w5em). GT4 and GT5 have 24 hour races at Nurburgring and Le Mans, so if I'm reading it right (I never got that far) a strict 100% completion of GT4 would require 72 hours of endurance racing alone, twice at Le Mans and once at Nurburgring, and to complete the car collection you'd need to win at Nurburgring as well.

Someone mentioned Penn and Teller's Desert Bus? Back in 2009, "Alden S." posted an alleged Desert Bus speedrun of 1000 hours — specifically, 1001:15:06, or a little under 42 days. Many online sites repeat this story as truth.

However, the specific date Alden S. posted his speedrun was 2009-04-01, so, I think it was intended to be taken with a pretty big grain of salt. ;)

Someone is attempting a 100% run of Diablo 3 which includes all achievements, collectibles, and item collection of all unique Legendary, Ancient, and Primal items currently at 921hrs out of a estimated 6800hrs. Forum post with full rules from the runner

Pokemon Stadium Complete the game category took 19h 41m 57s