Log in with your Prime-enabled account or sign up for Prime. Click Continue  to begin the account-linking process. Click Go to Activision  to be redirected to Activision's account-linking page. Log in with your Activision account and authorize Prime Gaming to fulfill content.

One must log into their Amazon account with the Prime subscription to get the redemption code for free rewards. Copy the redeem code. Tap the //callofduty/redemption  and paste the redeem code in the text box.

According to Activision's post on X (formerly Twitter), the huge file size is due to the increased amount of content available Day 1,  which includes map files for Call of Duty: Warzone, support for Modern Warfare II items, and the new open-world Zombies mode.