Cosmic parallax is the predicted slow change over decades in the angular separation between distant sources on the sky if the large-scale expansion is anisotropic or significantly inhomogeneous, providing a direct real-time test of the FLRW assumption underlying ΛCDM (Quercellini et al. 2009; Räsänen 2014). In a perfectly homogeneous and isotropic FRW universe, apart from local peculiar motions, no cosmological parallax is expected, so any detected coherent signal—or even tight upper limits from missions like Gaia—puts pressure on ΛCDM extensions that invoke large voids, off-center observers, or anisotropic expansion to solve other tensions, because these scenarios often predict parallax amplitudes close to the observational bounds (Quartin & Amendola 2010; Ding & Croft 2010).