Angular momentum evolution and extra mixing are two of the greatest uncertainties in stellar models of evolved stars. Subgiant stars are the transition between the main sequence, where models are properly calibrated, and the red giant branch phase, where models deviate from observations. As such, they work as anchoring points to study rotational and chemical evolution in evolved stars. Asteroseismology, enabling the measurement of core rotation, masses, and radii, has revolutionized our understanding of stellar physics. With TESS and high-resolution spectral follow-up, we can map the transport of angular momentum and material in stellar interiors during this transitional phase, providing a basis to identify changes taking place in the giant branch and improving stellar evolutionary models.
