The Diablo 4 Season 4 content was announced days ago. The overhaul to the core mechanics is so comprehensive. Among the highlights are major changes to the game's itemization and various other adjustments that will become permanent features. Here are all the confirmed changes for Diablo IV Season 4.

Item Update Changes 

    There will be less loot dropping, but the quality will be better. The idea is for players to improve their gear through crafting.
    Many unnecessary affixes have been removed from the game.
    Relevant affixes will be adjusted to make a more significant impact.
    Items stats are simplified to straightforward bonuses such as increased damage and health.
    Items with attributes like intelligence and strength will only drop for the classes that benefit most from them.
    Every Legendary feature in the game will be accessible in the Codex of Power.
    Salvaging Legendary items will add the best attribute rolls to your Codex of Power, allowing for unlimited use on other items.
    Legendary or Unique items can now be traded, but modifying them will make them untradeable. This means you can buy D4 items with Legendary or Unique easily.
    Different tiers of items will drop in different World Tiers, which means Sacred items will drop only in World Tier 3, while Ancestral items will drop only in World Tier 4.
    Legendary items will now have 3 affixes instead of 4, and rare items will have 2 affixes instead of 4.
    Legendary items dropped from high-level monsters will have a fixed item power.
    Gems have been simplified and strengthened.
    There's now a cap on gold costs for rerolling items at the Occultist.
    Some crafting materials have been combined and reduced.
    Forgotten Souls will now drop from Whispers and occasionally from Elites.
    More Unique items can drop into lower World Tiers (i.e., World Tiers 1 &2), and all Unique items can drop into higher World Tiers.
    Uber Unique items will start dropping from level 55 monsters.

Loot Upgrading Changes

    Defeat a boss to get gloves with three stats on them. (Legendary and Rare items now have one fewer stat.)
    The gloves are nearly perfect but require Tempering at the blacksmith.
    Use a new 'manual' item found to add one of four mobility-based stats (e.g., movement speed, evade cooldown reduction, etc.).
    Luckily, add the movement speed stat to your item before using up its maximum Temper rerolls.
    Add one more stat to upgrade your Bone Splinters skill, causing it to shoot more projectiles.
    Use the newly introduced Masterworking system to enhance all attributes, including those that have been tempered, on the gloves for up to 12 enhancements.
    If luck is on your side, roll the four significant upgrades to your movement speed, substantially increasing the stat (one stat jumps up every four upgrades).

Crafting System Changes

    Tempering introduces a new crafting system, allowing players to add fresh attributes to their gear.
    Tempering Manuals offer one of four attributes randomly to an item and are acquired from various in-game content.
    Ancestral items can incorporate up to two Tempered attributes from different categories.
    Diablo 4 Items have a limited Tempering Durability, indicating how many times a Temper can be altered.
    Masterworking introduces a new late-game item enhancement system featuring 12 ranks.
    Masterworking boosts the values of current attributes, with most ranks slightly boosting all attributes and a significant upgrade to one attribute every four ranks.