Velocity-exact cubic-in-spin radiated Lorentz charge of two Kerr black holes at third post-Minkowskian order

We compute the cubic-in-spin contribution to the radiated Lorentz charge in two-Kerr-black-hole scattering at O(G3), for generic spin orientations and arbitrary masses, exactly in the relative Lorentz factor σ. All four cubic-spin partitions are included. The calculation uses the specified dimensionally continued worldline source R16/P0, the d branch, the covariant spin supplementary condition, and the de Donder charge at the energy-weighted incoming origin. The zero-frequency completion is obtained from the 2PM impulse using the leading-soft functional, with the same-endpoint prescription of Di Vecchia, Heissenberg and Russo. A regulated soft-limit argument excludes additional spin-dependent endpoint data under the stated assumptions. Independent calculations reproduce the total spatial charge at p∞1 and p∞3, its boost components at p∞0, and the accompanying energy and momentum at the stated leading and next spatial orders. A blinded comparison includes the first nonzero octupole momentum coefficients. Separately computed mixed sectors satisfy origin translation and body exchange exactly in velocity. These checks validate the result at the specified PN orders; they do not constitute independent validation at arbitrary velocity. This deposit contains the 68-page manuscript and its LaTeX source archive, including exact cubic-spin coefficient data, conventions, a Python reader, examples, and validation information as scientific ancillary files.