The rpm-ostree-libs package includes the shared library for rpm-ostree.
acquired package info from repodata DB: repodata/750d2b47baac9c5cbb3ae49bbf8c4ff7bf44796813ecb397af35aa5323864a72-primary.sqlite.bz2
The rpm-ostree-devel package includes the header files for rpm-ostree-libs.