The intensity interferometry technique enables telescopes to achieve exceptionally high angular resolutions, on the order of hundreds of microarcseconds, in the optical range. I will explain how, in contrast to traditional phase interferometry, this technique readily accommodates blue and near UV wavelengths, and is straightforward to expand to longer telescope baselines with the potential to reach angular resolutions of a few microarcseconds for baselines of a few kilometers. In addition to its regular gamma-ray observations, we have been operating MAGIC as an optical interferometer for several years. We have recently measured the diameters of 13 early-type stars that lacked prior measurements. In addition, in 2024 we have extended the same technical solutions to the first CTA Large-Sized Telescope operating at ORM, LST-1. I will present these observations, delineate plans for the upcoming upgrades to the four LSTs currently under deployment, and describe a science cases that are within reach during the next few years, among others the study of early type stars, fast rotators, and expansion of novae.