  Fermi surface reconstruction in cuprates can lead to an abrupt change in the
Fermi momentum $k_F$ between different phases. This phenomenon remains subject
of debate and is at the heart of an ongoing discussion about the nature of the
metallic state in the pseudogap regime. Here we study a minimal model of a
$k_F$ changing crossover in the one-dimensional Fermi-Hubbard model, where a
tuning of the onsite interaction leads to a crossover between a spin-$1/2$
Luttinger liquid with small Fermi momentum and a spinless chargon liquid with
large Fermi momentum. We attribute this to an emergent $U(1)$ symmetry in the
strongly correlated limit, which can be used to derive a modified Luttinger sum
rule recovering the large Fermi momentum. We analyse Friedel oscillations at
the edge of a system to directly probe the change of Fermi momentum at zero and
non-zero temperature. This paves the way for a direct experimental observation
of changes of the Fermi momentum using ultracold fermions in a quantum gas
microscope, with possible extensions to higher dimensional systems.
