  Implementation of high-fidelity two-qubit operations is a key ingredient for
scalable quantum error correction. In superconducting qubit architectures
tunable buses have been explored as a means to higher fidelity gates. However,
these buses introduce new pathways for leakage. Here we present a modified
tunable bus architecture appropriate for fixed-frequency qubits in which the
adiabaticity restrictions on gate speed are reduced. We characterize this
coupler on a range of two-qubit devices achieving a maximum gate fidelity of
$99.85\%$. We further show the calibration is stable over one day.
