Cui, 68, whose time in Washington spanned the presidencies of Barack Obama, Donald Trump and Joe Biden, has been witness to a profound shift in US-China relations. During his tenure, Beijing has grown increasingly confident and assertive, demanding that it is treated as an equal. Washington, on the other hand, has become wary of China's rise, seeing it as a strategic rival and potential threat to the US-led world order.
"Relations between China and the US are at a critical crossroads, with the US engaging in a new round of restructuring in its government policy towards China, and it is facing a choice between cooperation and confrontation," Cui wrote in afarewell letter published on the embassy's website Tuesday.
And until his yet-to-be-announced successor arrives, neither Beijing nor Washington will have a top envoy in each other's capital.
The former US ambassador to China, Terry Branstad, left Beijing last year before the November election. Nicholas Burns, a former diplomat, is a top contender to fill the role, but the Biden administration has yet to make a formal announcement.