Let's take a look at the download size of Siege of Paris to help you make sure you're prepared for its launch.
Assassin's Creed Valhalla - Siege of Paris Download Size
The Siege of Paris DLC comes in at slightly different file sizes across PlayStation, Xbox and PC. This is fairly standard as it will come down to what files are required as well as the optimisation of the update, and general game, on all platforms.
The PC version is as of yet unconfirmed but believed to be close to the 30GB mark. This could, however, be misleading and be a case of the update appearing to be once size, but actually removing certain files from the base game which ends up with a net GB loss of around 15GB.
Once we have an official confirmation of the PC update size we'll keep you posted. It's very possible that the update on all three platforms is similar, but the way the PC update is handled give off the overall impression that it's much bigger.
This also happens in a lot of Battle Royale games like Warzone and Apex Legends, where a patch may be advertised as 32GB or more, but only actually take up an extra 10/15GB on the hard drive due to optimisation and file replacement or removal.