Power armor is one of the most iconic element of the Fallout series, with the helmet of the T-51b being on the box art of the first game, and associated with the franchise ever since. Every time new players jump into a Fallout game, the first thing they want is power armor - but these advanced outfits are among the most powerful in each game, and you'll need to put some legwork in if you want one.
What is the X-01 Power Armor?
The X-01 power armor is a returning design from Fallout 2, where it was known as the Advanced Power Armor and associated mostly with the Enclave, the questionably motivated remnants of the pre-war US Government. The design seen in Fallout 4 is more faithful to this original design than the variant we saw back in the Fallout 3 days, and looks like an exact and authentic recreation in much greater detail.
Power armor works very differently in Fallout 4 from a gameplay perspective than it did in previous installments, and is more akin to the lore surrounding how this technology is intended to work. Players will need a Power Armor Frame onto which individual pieces of the X-01 can be attached, as opposed to the X-01 coming as a complete set - though in rare cases you can find an entire suit in one place.
Like other power armor parts, the elements of the X-01 spawn randomly in MK. I to MK. VI variants depending on your level and what DLCs you have installed. In the base game, MK. III is the limit. The higher this number, the better the stats - that said, overall the X-01 is one of the strongest power armors in the game, so wearing it will give you a clear advantage.
Finding the Pieces of the X-01 Power Armor in Fallout 4
Parts of the X-01 will only start spawning once you have reached level 28 with your character. The higher your level, the better your chances are of higher mark-numbers spawning, so don't expect to bumble into an MK. III piece as a fresh level 28.
The only exception to this rule is an X-01 Helmet that can be stolen at any time from Proctor Teagan's shop located onboard the Prydwen, which is behind a door with a Master level lock. If you try and steal the helmet, make sure you aren't discovered - there are few safe ways off an airship!
There are a number of locations where you can find a full X-01 armor set throughout the Commonwealth.
There is an unmarked building in Boston guarded by automatons that hides a full set. Travel to Goodneighbor first, then head east towards the coastline until you reach Custom House Tower. Standing in front of the entrance and facing away, you'll see a pair of teal buildings - you need the one further away. You'll know you are in the right place if you see a large sign reading "35 Court".
You need to go up the elevator here which will take you to one of the floors midway up the building, where you have to get out and look for another elevator. There is an Assaultron and a Sentry Bot here that will attack you on sight, so be prepared.
Once you are done fighting, head up to the roof with the second elevator, and you'll find a complete X-01 power armor suit in a stasis chamber.
National Guard Training Yard
This location isn't a guaranteed spawn, but there is a good chance a full set will be waiting in a Master locked room at the National Guard Training Yard, while another can spawn in a pile of shipping containers just outside this location.
Nuka-World Power Plant
Not one, but two full sets are located at the power plant. The first one is in a power monitoring station southeast of the plant proper, while the second is found inside the terminal locked basement inside the power plant.
Dry Rock Gulch
You can find a full set just lying out in the open on a flatbed truck westward of Dry Rock Gulch.