Is it official? No. But it's stable, lightweight (under 6MB), and legally ambiguous—though Yamaha has not issued takedowns, likely due to the age of the technology and the fact that the original ROM data is not redistributed (the plugin reads your legally owned S-YXG50 .SYX or .TBL files).
A GitHub project ( xg-emu ) emerged in late 2024. It aims to emulate the Yamaha MU1000 DSP in software. As of early 2026, it can load original XG firmware dumps and render basic voices, but it is not a VST , has no GUI, and polyphony is limited to 32 voices. It requires compiling from source. Potential future VST, but not ready. yamaha xg vst 64 bit new