  Magnetic-field-resilient superconducting circuits enable sensing applications
and hybrid quantum-computing architectures involving spin or topological qubits
and electro-mechanical elements, as well as studying flux noise and
quasiparticle loss. We investigate the effect of in-plane magnetic fields up to
1 T on the spectrum and coherence times of thin-film 3D aluminum transmons.
Using a copper cavity, unaffected by strong magnetic fields, we can solely
probe the magnetic-field effect on the transmons. We present data on a
single-junction and a SQUID transmon, that were cooled down in the same cavity.
As expected, transmon frequencies decrease with increasing fields, due to a
suppression of the superconducting gap and a geometric Fraunhofer-like
contribution. Nevertheless, the thin-film transmons show strong magnetic-field
resilience: both transmons display microsecond coherence up to at least 0.65 T,
and $T_1$ remains above 1 $\mathrm{\mu}$s over the entire measurable range.
SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude
that thin-film aluminum Josephson junctions are a suitable hardware for
superconducting circuits in the high-magnetic-field regime.
