© 2018 IOP Publishing Ltd. We report on remarkably high in-field performance at 4.2 K achieved in >4 μm thick rare earth barium copper oxide (REBCO) samples with Zr addition. Two different samples have been measured independently at Lawrence Berkeley National Laboratory and the National High Magnetic Field Laboratory, achieving critical current densities (J c) of 12.21 MA cm-2 and 12.32 MA cm-2 at 4.2 K, 14 T (), respectively, which corresponds to equivalent critical current (I c) values of 2247 and 2119 A/4 mm. These I c values are about two times higher than the best reported performance of REBCO tapes to date and more than five times higher than the commercial HTS tapes reported in a recent study. The measured J c values, with a pinning force of ∼1.7 T N m-3 are almost identical to the highest value reported for thin (∼1 μm thick) REBCO at the field and temperature, but extended to very thick (>4 μm) films. This results in an engineering current density (J e) above 5 kA mm-2 at 4.2 K, 14 T, which is more than five times higher than Nb3Sn and nearly four times higher than the highest reported value of all superconductors other than REBCO at this field and temperature. The reported results have been achieved by utilizing an advanced metal organic chemical vapor deposition system. This study demonstrates the remarkable level of in-field performance achievable with REBCO conductors at 4.2 K and strong potential for high-field magnet applications.