  A small-$x$ helicity evolution has been derived in 2016-18 and received an
important modification in 2022. This article discusses its general framework
and summarizes the recent theoretical developments, including the asymptotic
behaviors of helicity PDFs and $g_1$ structure function at small $x$. The
latest fits to various polarized scattering data are also discussed. The
results from this research program will provide important theoretical inputs
for the future polarized small-$x$ measurements at the electron-ion collider
(EIC).
