  We consider the 1d interacting Bose gas in the presence of time-dependent and
spatially inhomogeneous contact interactions. Within its attractive phase, the
gas allows for bound states of an arbitrary number of particles, which are
eventually populated if the system is dynamically driven from the repulsive to
the attractive regime. Building on the framework of Generalized Hydrodynamics,
we analytically determine the formation of bound states in the limit of
adiabatic changes in the interactions. Our results are valid for arbitrary
initial thermal states and, more generally, Generalized Gibbs Ensembles.
