Fallout 76 will receive a patch on release. The Day-1 patch will be substantial and will require more storage space than the game itself.
When does Fallout 76 release? On November 14, it is the release day of Fallout 76. Prior to that, players can already download a Day-1 patch.
Some of you might need to make space for it, as the Day-1 patch will be huge and will take up even more storage space than the main game itself.

Fallout 76 will be a chunk on your hard drive
This is how much storage you will need for Fallout 76: The main game itself will be around 45 GB in size. This size is also the same as the beta of Fallout 76. While your progress from the beta will carry over, you will still need to reinstall the game on PS4 and Xbox One. PC players only need to download a small patch.
You will also need to download the large patch that came with the beta again. Depending on the platform, this will be between 30 and around 40 GB in size.
Together with the Day-1 patch, that brings the size to about 55 GB. Overall, you will need nearly 100 GB of storage space for Fallout 76 including the patch. We will only have precise numbers on that once the pre-load for PC and PS4 starts. Fallout 76 can already be downloaded on Xbox One.

What does the patch change? There are no exact details yet. Presumably, it will involve bug fixes and performance optimizations, as in the beta patch.
This is already the second 100 GB chunk in a short time, as Red Dead Redemption 2 was released on October 26. The open-world giant also requires over 100 GB of hard drive space. However, the game did not even require a patch, RDR2 was delivered with two Blu-Ray discs right from the start.