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

We report extended MCMC constraints on the Stratoverso cosmological model, a scalar-field extension of ΛCDM featuring a late-time kinetic transition. With respect to v2, three major improvements are presented: (1) a C¹-smooth implementation of the conformal reset that eliminates the spurious late-time ISW instability affecting earlier versions; (2) a substantially longer MCMC exploration (runs v4+v5, >21,000 accepted samples) identifying a deeper posterior minimum; (3) a partial resolution of the Hubble tension. The model preserves early-time physics exactly as in ΛCDM — including the CMB acoustic scale and the age of the universe (13.754 Gyr) — while modifying the cosmic expansion only at z < z_trans via a smooth sigmoid transition. A full MCMC analysis on Planck 2018 (TTTEEE + lensing), DESI DR2 BAO, and Pantheon+ yields χ² = 2421.2 versus χ²_ΛCDM = 2497.5, giving Δχ² = −76.3, ΔAIC = −72.3, ΔBIC ≈ −60. The improvement is distributed across all datasets. The Hubble constant is shifted to H₀ = 67.71 ± 0.54 km/s/Mpc (best-fit 68.28), above the Planck ΛCDM value, providing a partial mitigation of the Hubble tension. The posterior disfavours λ_reset = 0 at >2σ, indicating a statistical preference for conformal resets over standard ΛCDM. Per-parameter convergence: R̂−1 < 0.1 for all physically relevant parameters (H₀: 0.069, λ_reset: 0.071, g_holo: 0.077). Full convergence (R̂−1 < 0.01) with multiple parallel chains is in progress and will be reported in a forthcoming PRD submission.