Hackers gained access to AMD's servers and stole a series of "test files" for current and future AMD graphics processors, including those in the Xbox Series X

According to AMD (via Engadget), the hackers were notified of the security breach in December 2019

The company's full statement is here:

AMD has not revealed exactly which files or which graphics cards were affected, but the TorrentFreak is a current Navi 10 architecture, future Navi 21, and the supreme treasure, the Arden GPU TorrentFreak obtained a message from the alleged intruder claiming to contain source code for the current Navi 10 architecture, the future Navi 21, and the crown jewel Arden GPU

Arden is the graphics processor unit of the Xbox Series X, a powerful chip that is said to shatter the performance of the PS5, according to these purportedly leaked benchmarks The GPU is based on AMD's RDNA 2 architecture and is rumored to run on 16GB of GDDR6 RAM and deliver 12 teraflops of computing power

On TorrentFreak, the alleged hackers claim they are seeking $100 million for the code they say they stole in November; AMD says it is "working closely with law enforcement authorities and other experts as part of an ongoing criminal investigation"