Version 1.1.15 was a stable release that introduced and refined several key features that distinguish Spire from competitors like Serum or Massive:

Reveal Sound Spire v1.1.15: Precision Engineering for Modern Producers Reveal Sound Spire

in v1.5.17, though v1.1.15 remains the definitive version for users maintaining older project compatibility. Changelog for «Spire» - Reveal Sound

: Compatible with VST, AU, and AAX formats in both 32-bit and 64-bit (PC only for 32-bit).