The β→ω transformation in metastable β titanium alloys plays a key role in defining their microstructure and mechanical properties. This presentation revisits ω phase formation in Ti–Mo alloys and introduces a new phase‑field model capable of capturing key experimental features that existing models fail to reproduce - especially the nanoscale size of athermal ω, the absence of direct ω - ω interfaces, and the coexistence of β and ω after quenching. The model incorporates a novel “double‑ditch” formulation with a penalization term that enforces separation of crystallographic variants without breaking the phase‑field formalism. Chemical‑composition fluctuations, generated from realistic short‑range-ordered solid solutions, emerge as the dominant factor enabling ω nucleation, whereas elastic contributions remain minor. 3D simulations are capable of producing realistic microstructures at nanoscale. New synchrotron XRD measurements (ESRF) support the predicted ω size (≈2.5–3.5 nm) and interface thickness. Altogether, the work provides a physically grounded modeling framework for athermal ω formation and establishes a basis for future extensions toward isothermal ω and multiscale simulations.