  The 1S hyperfine splitting in hydrogen is measured to an impressive ppt
precision and will soon be measured to ppm precision in muonic hydrogen. The
latter measurement will rely on theoretical predictions, which are limited by
knowledge of the proton polarizability effect $\Delta_\text{pol}$. Data-driven
evaluations of $\Delta_\text{pol}$ have long been in significant tension with
baryon chiral perturbation theory. Here we present improved results for
$\Delta_\text{pol}$ driven by new spin structure data, reducing the
long-standing tension between theory and experiment and halving the dominating
uncertainty in hyperfine splitting calculations.
