This is part IV https://zenodo.org/records/16978234 This is part II https://zenodo.org/records/16978117 This is Part III [https://zenodo.org/records/16978002] This work demonstrates that the observable universe can be consistently interpreted as the interior of a black hole, with Schwarzschild radius equal to the Hubble radius (rs = rh = c/H0). Under this identification, the holographic bound is exactly saturated: Imax = 3.04 × 10¹²² bits. By calculating baryon information content with realistic temperatures from WHIM observations, we show that particle contributions (≈10¹⁰⁴ bits including SMBHs) fall 18 orders of magnitude short of the holographic bound. The missing information must be carried by vacuum entanglement across the horizon, as required by the Bekenstein–Hawking formula. The cosmological constant decomposes naturally into Λgeom = 8.59 × 10⁻⁵³ m⁻² (78%) from the LTB metric and Λinfo = 2.46 × 10⁻⁵³ m⁻² (22%) from information saturation effects. This “Λ split” simultaneously determines the observed CMB temperature (via horizon entanglement and exponential enhancement e⁶⁹), the proper-time age gradients explaining JWST’s mature galaxies, and the amplitudes of the Hubble and S₈ tensions. Falsifiable predictions include negative redshift drift ( ˙z = −1.23 × 10⁻¹⁰ yr⁻¹ at z = 1), near-solar metallicities at z > 10, enhanced stellar populations (Dn4000 > 1.5 at z = 7), and a 2.8% Hubble diagram dipole from our off-center position. This framework unifies holography, black hole thermodynamics, and cosmological anomalies into a testable black hole universe paradigm.