After more than a year of haggling over the details, Russia has agreed to sell China 24 Su-35 fighters. The big obstacle to this sale was the Chinese inability to assure Russia that the new Russian technology in these aircraft would not be stolen by Chinese aviation firms. Apparently a mutually agreeable compromise was worked out.
At first China refused to buy Su-35 fighters from Russia if a "no unauthorized duplication" clause was included in the contract. The Chinese wanted to buy the Su-35s but were not willing to sign a binding agreement to not copy the Russian design. China is already producing unauthorized copies of the Russian Su-27, as the J11 and Russia is not happy with that at all. China has since designed a two-seat fighter bomber version (the J16), a stealthy version (J17), and obtained an aircraft carrier version of the Su-30 (the Su-33) from Ukraine and are producing a copy (as the J15).
China insists these are all Chinese designs that just happen to bear some resemblance to Russian fighters. In response Russia halted combat aircraft sales to China but still sold jet engines for these aircraft. So far, China has been unsuccessful in building copies of these engines. The engine sales are too lucrative to pass up, as they enable the Russian engine manufacturers to continue developing new designs. The Chinese plan to steal these as soon as they figure out how to handle the exotic manufacturing skills required to build these engines.
The Su-35 is a 34 ton fighter that is more maneuverable than the original, 33 ton, Su-27, and has much better electronics. It can cruise at above the speed of sound. It also costs at least fifty percent more than the Su-27. That would be some $60 million (for a barebones model), about what a top-of-the-line F-16 costs. The Su-27 was originally developed to match the F-15, which is larger than the single engine F-16. The larger size of the Su-27/35 allows designers to do a lot more with it in terms of modifications and enhancements.
The Su-35 has some stealth capabilities (or at least be less detectable to most fighter aircraft radars). Russia claims the Su-35 has a useful life of 6,000 flight hours and engines good for 4,000 hours. Russia promises world-class avionics, plus a very pilot-friendly cockpit. The use of many thrusters and fly-by-wire will produce an aircraft even more maneuverable than Su-30s (which were Su-27s tweaked to be extremely agile). The Su-35 was in development for two decades before it was declared ready for production in 2005. But even then there were problems with the new engines that gave it its superior performance. Russia says the engine problems are solved, but only time will tell if that is true.
The Su-35 is not meant to be a direct rival for the F-22 because the Russian aircraft is not nearly as stealthy. The Su-35 carries a 30mm autocannon (with 150 rounds) and up to eight tons of munitions, hanging from 12 hard points. This reduces stealthiness, which the F-22 and F-35 get around by using an internal bay for bombs and missiles. But if the maneuverability and advanced electronics of the proposed Su-35 live up to the promises, the aircraft would be more than a match for every fighter out there except the F-22. Since the Su-35 is to sell for well under $100 million each, there should be a lot of buyers.
Meanwhile, China has not had an easy time with its Su-27 clone, the J11. This aircraft entered service in 1998, but production was very slow and only a hundred were produced. It was during this process that the Chinese mastered many of the technical details of building and modifying the Russian aircraft. China then modified the Su-27 design and produced at least a hundred of the 33 ton J11A. This model was equipped with modern, Chinese made, electronics and is capable of hauling eight tons of radar guided air-to-air missiles and smart bombs. Then came the J11B, which was the same size and weight as the J11A but had a more capable AESA radar and is intended to specialize in air-to-ground missions, while also being able to take care of itself in air-to-air combat.
The Su-35 would give China a lot of ideas (and technology) for the J11C, no matter what promises were made to the Russians.