Diablo 4's first hotfix buffs enemies in the difficulty level you probably haven't even played yet

pcgamer.com:

Less than 24 hours after the start of its early access release, the first Diablo 4 hotfix is live. The update makes minor nerfs to the Sorcerer and Rogue classes, and makes life more difficult for everyone by increasing the health of monsters at higher World Tiers.

Diablo 4 World Tiers are essentially difficulty levels. But the system is a little more restrictive than many other games: To begin, you only have access to two levels, Adventurer and Veteran—basically your «easy» and «normal» levels. World Tier 3 (Nightmare) and World Tier 4 (Torment) don't become available until after you've completed the campaign.

Moving to higher World Tiers increases both the challenge and the reward: At World Tier 3, for instance, you'll get a 100% XP bonus, but your non-physical resistances are reduced by 20% and the difficulty of enemies is increased. But apparently not quite enough, as Blizzard has now given them a bit of a health boost.

Rogues have been very slightly dialled back in the hotfix, as there will now be a brief delay in marking enemies after their Inner Sight's unlimited energy expires, while the sorcerer's Flame Shield will be put on full cooldown when it's put into an Enchantment slot, so you'll have to wait a bit before you can use it.

There's no indication as to exactly which World Tiers will have healthier monsters, but the general feeling on Reddit is that it will be W3 and W4, as the first two tiers are available immediately and not «later.» I've reached out to Blizzard to clarify, but frankly I think Reddit's probably right.

The Diablo 4 hotfix, which takes the game to version 1.0.2, is a server-side patch, which means you don't have to do anything—it's already done. You can check out the full, very brief patch