First spotted by Chinese observers in 2010, the J-20 was later shown to the public for the first time in 2016.
The J-20 was initially equipped with fourth-generation WS-10G engines, which were based off Russian AL-31s. But it has reportedly since been equipped with true fifth generation WS-15 Emei engines comparable to the F-22's F119 engines.
Several reports even suggested that the J-20 had been equipped with WS-15 Emei engines during military drills at the Zhurihe base in 2017.
Source: The Diplomat, AsiaTimes
The WS-15 engine is rumored to have a maximum thrust of 44,000 lbs, compared to the Raptor's 35,000 lbs of thrust.
Source: The Diplomat, Business Insider, AsiaTimes
The WS-15 engines can reportedly supercruise, meaning that they can fly at supersonic speeds without using its afterburners.
Source: CSIS
But other analysts and reports contradict whether the WS-15 is operational, saying that the Chinese have had major problems testing it and the new engine won't be installed on the jet until 2020.
Source: Business Insider
"At the core of every plane is the engine — it's all about the engine," Michael Kofman, a senior research scientist at CNA, previously told Business Insider. "Everything else may be interesting, but it's all about the engine."
Source: Business Insider
The J-20's stealth capabilities have also been called into question.
"You see how large it is? It's got so many surfaces, and a lot of them look pretty reflective from the sides too," Kofman told Business Insider. "I'm pretty skeptical of the stealth on that aircraft."
An aircraft is stealthy if its shaped in a way that reflects radar signal or covered in a material that absorbs the signal.
Retired US Air Force Lt. Gen. David Deptula said in late 2016 that the J-20 "may have some significant low-observable capabilities on the front end, but not all aspects."
"It's apparent from looking at many pictures of the aircraft that the designers don't fully understand all the concepts of LO design," one Lockheed Martin scientist previously told Business Insider, referring to low-observable, or stealth, design.
Source: Business Insider
At the same time, it was recently reported that the J-20 might be equipped with metamaterial absorbers that can absorb radars from enemy fighters and missiles.
Source: Popular Science
As for weapons, the J-20 has two lateral bays for small air-to-air missiles and a larger bay beneath the fuselage for other missiles.
The J-20 is also expected to be able to carry ramjet powered versions of the PL-21 and PL-12D air to air missiles.
Source: The Diplomat, CSIS
But whatever the J-20's current and future capabilities are, analysts appear to agree that the J-20 is equipped with quality avionics and software.
The J-20 is "slated to carry a variety of advanced electronic systems," CSIS reported in 2017.
"This technology includes an active electronically scanned array, a chin mounted infrared/electro-optic search and track sensor, and a passive electro-optical detection system that will provide 360° spherical coverage around the aircraft. These systems are expected to be comparable to those found inside the F-35."
Source: Business Insider, The Diplomat, CSIS
Most analysts also seem to agree that the J-20 was not meant to compete with the F-22 as a dogfighter.
The J-20 is "not a fighter, but an interceptor and a strike aircraft" that doesn't seek to contend with US jets in air-to-air battles, Malcolm Davis, a senior analyst at the Australia Strategic Policy Institute, previously told Business Insider.
Still, as Abraham Ait noted in The Diplomat, because the F-22 program has been terminated, the J-20 might supersede it rather quickly.
"The pace at which the Chinese fighter’s capabilities are improving far exceeds those of the F-22," Ait writes.
China is also developing another stealth fighter, the J-31, which first flew in 2014, and will be part of a new "family" of Chinese aircraft.