Deep surveys, especially with JWST, have identified surprisingly massive, compact galaxies (stellar masses up to ?10¹°–10¹¹ M?) at redshifts z ? 7–10, implying that substantial stellar mass assembled within a few hundred million years of the standard Big Bang clock (Labbé et al. 2023; Boylan-Kolchin 2023). In ΛCDM, forming enough massive dark matter haloes and then converting a large fraction of their baryons into stars so quickly pushes against halo mass function limits and requires star-formation efficiencies and duty cycles that are uncomfortably high, leading to concerns that either early galaxy formation physics or the underlying cosmology needs revision (Boylan-Kolchin 2023; Shen et al. 2024).