The term "AetherSX3" is an unofficial, fan-coined label. No legitimate build bearing that exact name has ever been released by the original developer. Instead, the "exclusive" refers to a series of of AetherSX2 that Tahlreth created for a select group of testers before his departure.
While it can't rewrite the core (which is closed source), it optimizes settings and restores frontend support for launchers. 3. The Future: PS3 and Beyond aethersx3 emulator exclusive