Oxygen has an impact on crystallisation in many metallic glasses. It is known to contaminate the powder used during manufacturing and enhance devitrification. In the extensively studied AMLOY-ZR01, the Cu2Zr4O type structure has been identified to form when oxygen is present. However, limited research of how oxygen impact the structural phase evolution has been made. We have carried out combined in situ highly time-resolved SAXS and WAXS measurements during flash-annealing of the Zr-based bulk metallic glass (BMG) AMLOY-ZR01 at the Swedish Materials Science beamline P21.2 at DESY Hamburg. After devitrification the local microstructure was analyzed with TEM and EDX. The devitrification is further investigated by performing dedicated numerical simulations based on the classical nucleation and growth theory (CNGT) with thermodynamics coupled to the CALPHAD framework. Homogeneous and heterogeneous simulations are performed to mirror our experimentally findings. The new insight into the devitrification and crystallisation of this alloy will be presented in this contribution.