The Witcher 3's Day One Patch is 482MB on PS4, 588MB on Xbox One

PS4 players picking up The Witcher 3: Wild Hunt tomorrow will need to download a 482MB day one patch to help resolve performance issues noted in early reviews.
As well as improving "overall performance", tidying up quests and fixing "multiple stability issues", the patch also introduces support for additional DLCs - presumably linked to the 16 free pieces of content due to roll out shortly after launch. 
The full PS4 patch notes can be seen below.
Major changes:

• Support for DLCs
• Multiple stability issues fixed
• Overall performance improvements

Quests and game:

• Variety of cosmetic quest improvements
• Journal objective fixes
• Quest mapping fixes
• Dialogue flag fixes
• Quest balancing issues
• Scene triggering improvements

Gameplay systems:

• Boat behaviour
• AI improvements
• NPC spawn strategy improvements
• Combat balancing
• UI optimizations

The Xbox One patch, meanwhile, comes in at 588MB, and introduces support for dynamic resolution scaling, alternating the resolution between 900p and 1080p in response to the game's demands. The game is believed to run at native 1080p on PS4 throughout.  The Witcher 3: Wild Hunt lands on PS4, Xbox One and PC tomorrow.