is xerath a late game or early game champion

He doesn't really spike. He gains consistent power over the course of the game.

He has a pretty consistent power curve honestly. He isn't super weak early and isn't super terrifying late until he has 600-800 ap, and at that point every mage is that terrifying.

Like most poke mages, he powerspikes significantly when he completes his Athene's. After that, it's about how you'd expect - bump at needless, bump at deathcap, bump at void staff, etcetera.

He's theoretically quite strong late game, since his kit offers LeBlanc levels of burst from relative safety. He's very vulnerable to being jumped on, tho, which makes his late game not stunning against hard engage champs.

His range gives him the ability to build 6 damage items. This gives him a very intimidating late game if he can position well.

as said, he's pretty consistent.

he's basically as strong in lane as your opponent is weak. he can force someone to farm under turret but you can't really assume he will get kills due to a reliance on skillshots and the ability to dodge them.

he cant roam very well but he makes up for that with absurd turret defense so his midgame isnt weak

late game his q does like 500 damage so he's very strong

id say he starts out above average in strength, loses a little in the midgame, and ends the game very strong

Others already said it, but Xerath's power scaling is a pretty even curve throughout the game. His power output isn't directly predicated by any of the items in his build, it's just an overall easy curve.