SinoSoldier
Colonel
Simple: just check Sukhoi's website.
A piece of news as major as the Chinese becoming the first customer of the Su-35 would definitely be on their front pages. When the Chinese negotiated with Antonov regarding the An-225, it was reported by the company even at the rumor stage. The fact that Sukhoi has made no mention of the Su-35 deal, even after all these years, is highly indicative of the Su-35 deal being nonexistent.
A piece of news as major as the Chinese becoming the first customer of the Su-35 would definitely be on their front pages. When the Chinese negotiated with Antonov regarding the An-225, it was reported by the company even at the rumor stage. The fact that Sukhoi has made no mention of the Su-35 deal, even after all these years, is highly indicative of the Su-35 deal being nonexistent.