A systematic experimental study of the variations of superconducting transition temperature and critical‐current density is reported for in situ formed multifilamentary Cu‐Nb3Sn composites containing 10 at.% Nb and 2–3 at.% Sn annealed at either 650 or 700 °C. A particular emphasis was placed on the evaluation of uniformity, thermal stability, and mechanical strength. Critical‐current density was measured as a function of transverse magnetic field and was found to increase in samples measured in a bent position. The overall critical‐current performance is comparable to that of reinforced stabilized conventional composites. Large residual resistivity ratios are indicative of a clean high‐conductivity matrix surrounding each individual filament, an important requirement for thermal stability. High resistance to plastic flow in these composites is attributed to strong filament‐to‐matrix bonding and small interfilament spacing. The ultimate tensile strength at 77 °K reached a value of ∼100 ksi (690 MPa). The measured uniformity of both critical currents and mechanical properties is found to be consistent with microstructural observations. Finally, an overall comparison is made with conventional continuous‐filament superconducting composites.