  The primary challenge in the field of high-temperature superconductivity in
hydrides is to achieve a superconducting state at ambient pressure rather than
the extreme pressures that have been required in experiments so far. Here, we
propose a family of compounds, of composition Mg$_2$XH$_6$ with X$=$Rh, Ir, Pd,
or Pt, that achieves this goal. These materials were identified by scrutinizing
more than a million compounds using a machine-learning accelerated
high-throughput workflow. They are thermodynamically stable, indicating that
they are serious candidates for experimental synthesis. We predict that their
superconducting transition temperatures are in the range of 45-80K, or even
above 100K with appropriate electron doping of the Pt compound. These results
indicate that, although very rare, high-temperature superconductivity in
thermodynamically stable hydrides is achievable at room pressure.
