To manufacture almost fully dense components, electron beam powder bed fusion of Ti-6Al-4V is typically combined with post-heat treatment, such as hot isostatic pressing (HIP). The standard HIP treatment performed at 920°C and 100 MPa for 2 h results in coarsening of the microstructure and impacting the yield strength. A low-temperature HIP treatment performed at 800°C and 200 MPa for 2 h resulted in limited coarsening and comparable yield strength to as-built material. A coarser microstructure is detrimental to tensile properties. Tensile testing at different temperatures revealed that thermal activation of different slip systems could possibly affect the elongation behavior, demanding additional investigation. Performing in situ neutron time of flight diffraction during tensile testing provides data to analyze strain evolution and load partitioning in the crystal lattice, which includes the slip planes. A two-phase elastic–plastic self-consistent model has been used to analyze and compare the experimental results. The lattice strain evolution results indicated that the basal slip 0 0 0 2 was activated at 20°C while the pyramidal slip 1 0 1¯ 1 was first activated during loading at 350°C. Load partitioning results showed that the β phase endures higher stresses than the α phase in the plastic regime.