What are the restrictions?

Broadly speaking, the policy restricts the sale of GPUs and related technology to Chinese companies. The specifics remain unclear because (a) the Department of Commerce hasn't released its official press report yet and (b) licenses to sell compute to Chinese companies will be approved on a case-by-case basis.

Here's the NYTimes description of the restrictions:

Companies will no longer be allowed to supply advanced computing chips, chip-making equipment and other products to China unless they receive a special license. Most of those licenses will be denied, though certain shipments to facilities operated by U.S. companies or allied countries will be evaluated on a case-by-case basis, a senior administration official said in a briefing Thursday.

The restrictions limit U.S. exports of the cutting-edge chips called graphic processing units that are used to power artificial intelligence applications, and place broad limits on chips destined for supercomputers in China. The rules also ban U.S.-based companies that make the equipment used to manufacture advanced logic and memory chips from selling that machinery to China without a license.
Perhaps most significantly, the Biden administration also imposed broad international restrictions that will prohibit companies anywhere in the world from selling chips used in artificial intelligence and supercomputing in China, if they are made with U.S. technology, software or machinery. The restrictions used what is know as the foreign direct product rule, which was last utilized by former President Donald J. Trump to cripple Huawei.
Another foreign direct product rule bans a broader range of products made outside the United States with American technology from being sent to 28 Chinese companies that have been placed on an “entity list” over national security concerns.
Those companies include Beijing Sensetime Technology Development Co, a unit of major Chinese artificial intelligence company, SenseTime. Also included are Dahua Technology, Higon, IFLYTEK, Megvii Technology, Sugon, Tianjian Phytium Information Technology, Sunway Microelectronics and Yitu Technologies, as well as a variety of labs and research institutions linked to universities and the Chinese government.
The rules also restrict U.S. citizens from helping to develop the Chinese semiconductor industry to advanced levels. Earlier on

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