Crystallization of Cu_47.5Zr₄₈Al₄Co_0.5 metallic glass upon isokinetic and isothermal annealing is studied by conventional and ultrafast differential scanning calorimetry, resistive flash-annealing, and in situ high-energy X-ray diffraction. The fast-heating experiments of Cu_47.5Zr₄₈Al₄Co_0.5 metallic glass are complemented by in situ high-energy XRD studies of the undercooled liquid by using electromagnetic levitation. The combination of complementary techniques reveals a competition between the Cu₁₀Zr₇, B2 CuZr and τ₄ Cu₂ZrAl phases crystallization depending on heating rate and shows the specific role of Co alloying. A continuous-heating-transformation diagram for a heating rate exceeding six orders of magnitude, Φ = 0.0833 − 90 000 K s⁻¹, and a time-temperature-transformation diagram are constructed.