Evidence for a Late-Time Kinetic Transition Improving CMB, BAO, and Supernovae Simultaneously.

We report evidence for a robust likelihood valley in a hybrid late-time kinetic transition model (the "Stratoverso" framework). The model preserves early-time physics exactly as in ΛCDM — including the sound horizon, the CMB acoustic scale, and the age of the universe (13.841 Gyr) — while modifying the cosmic expansion only for z ≲ z_trans via a smooth sigmoid transition function. A full MCMC analysis on Planck 2018 (TTTEEE + lensing), DESI DR2 BAO, and Pantheon+ supernovae yields a total Δχ² = −19.3 relative to ΛCDM with two additional parameters, corresponding to ΔAIC = −15.3 and ΔBIC ≈ −3.7. The improvement is driven primarily by the CMB: the Planck high-ℓ TTTEEE likelihood improves from 633.8 to 604.5 (Δχ² = −29.3). The derived age of the universe at the best-fit is 13.841 Gyr, in excellent agreement with standard cosmology. Best-fit parameters: H₀ = 65.26 km/s/Mpc, λ_reset = 0.0520, z_trans = 0.1313, Δz = 1.011. These results are preliminary (chain not yet fully converged, R̂−1 ~ 0.2; standard threshold R̂−1 < 0.01) and are submitted to establish priority. A fully converged analysis is in progress.