All physical edition preorders of Call of Duty®: Modern Warfare® 4 include a code to register for Early Access to the Modern Warfare 4 Open Beta 1. In most cases, the code will be printed on the retail receipt or sent to you via email on an online receipt. Please contact your retailer if you didn't receive or can't locate your code.
If you preordered a digital edition of Modern Warfare 4, you don't need a code. You're automatically registered to participate in the Modern Warfare 4 Open Beta with Early Access on your preorder platform.