"At least six J-20s are in active service, with tail numbers 78271-78276 identified. Another six were believed ready to be delivered by end of Dec 2016.[86] On 9 March 2017, Chinese officials confirmed that the J-20 had entered service in the Chinese air force.
In September 2017, the J-20 officially entered military service with PLAAF, making China the second country in the world after United States wielding fifth-generation stealth aircraft, and the first in Asia.[87][87][88][16]
In January 2018, Chinese media reports that J-20 is in full operation-ready deployment.[89]"
https://www.economist.com/news/china/21737074-some-technolog...
"in two years’ time, if not before, America is likely to lose its monopoly of radar-beating stealth combat aircraft with the introduction into service of China’s Chengdu J-20. This has a much longer range than America’s new F-35 fighter and will be a serious threat to American warships in the Pacific."
"Another system, yet to be named, would provide China with an ability to knock out targets as far away as 400km, a far greater range than any other air-to-air weapon in service. It would threaten aircraft that currently operate safely from a considerable distance, such as tankers and planes used for airborne surveillance and control. "