  Joint analysis of the baryon acoustic oscillations (BAO) measurement by the
Dark Energy Spectroscopic Instrument (DESI) first data release, Type Ia
supernovae (SNe) of the Dark Energy Survey Year 5 (DES5YR) release and cosmic
microwave background (CMB) data favors a quintom-like dynamic dark energy model
over the standard Lambda cold dark matter ($\Lambda$CDM) model at $3.9\sigma$
level (Adame et al. 2024). We demonstrate that the preference for dynamic dark
energy does not rely on the detailed modeling of CMB physics and remains at
$3.2\sigma$ level when the full CMB likelihood is replaced by a CMB
acoustic-oscillation angle ($\theta_\star$) prior and a baryon abundance
($\Omega_bh^2$) prior. By comparing the data with over $10^4$
$\Lambda$CDM-based simulations, we find that both DES5YR SNe and DESI BAO
contribute significantly to the preference for dynamic dark energy. The
preference for dynamic dark energy is unlikely (probability $\lesssim 0.02$)
due to unknown systematics in DES5YR SNe and statistical fluctuations in DESI
BAO, or vice versa.
