MPK - Multi-Pack, a retailer would order a big box with several boxes of CPUs in it. BOX - CPU in a box with a cooler meant for consumers; possibly came from an MPK
"MPK" is a bare CPU that is typically sold to distributors and OEMs in "trays" of several hundreds or thousands
They're physically the same but the intended use case for MPK processors is for large-scale system integrators, who would presumably offer a warranty to their end users and in turn are reimbursed by AMD in aggregate via contractual terms.
As such, AMD explicitly states that they do not offer direct warranty support to consumers who buy individual MPK chips. To wit:
AMD’s warranty on processors only extends to customers who have purchased sealed, retail-packaged Processors in a Box.
Of course you may have recourse to some sort of warranty with the vendor you bought it from, but this is wholly dependent on both store policy and local laws.
