The Modules for Experiments in Stellar Astrophysics (MESA) have been significantly updated to enhance their capabilities in modeling giant planets, asteroseismology, rotation, and massive stars. These updates include improved modeling of giant planet evolution down to masses as low as 0.1 Jupiter masses, integration of the ADIPLS adiabatic pulsation code for asteroseismology, and a revised Ledoux criterion for better handling of composition gradients. MESA now supports the evolution of rotating stars, including angular momentum diffusion and chemical abundance diffusion, and allows for the continuous evolution of massive stars to core collapse. New treatments of radiation-dominated envelopes and improved solutions to stellar structure and composition equations have enhanced computational speed on multi-core processors. The MESA Software Development Kit (SDK) provides a unified build environment, and community tools enable rapid visualization of MESA results. The paper describes new capabilities in modeling giant planets, asteroseismology, and the evolution of massive stars, along with updates to physics modules, numerical methods, and visualization tools. MESA now includes detailed modeling of inert cores, irradiation effects, and surface heating, with applications to exoplanets and low-mass stars. The software has been validated against observational data and is used for a wide range of astrophysical studies.The Modules for Experiments in Stellar Astrophysics (MESA) have been significantly updated to enhance their capabilities in modeling giant planets, asteroseismology, rotation, and massive stars. These updates include improved modeling of giant planet evolution down to masses as low as 0.1 Jupiter masses, integration of the ADIPLS adiabatic pulsation code for asteroseismology, and a revised Ledoux criterion for better handling of composition gradients. MESA now supports the evolution of rotating stars, including angular momentum diffusion and chemical abundance diffusion, and allows for the continuous evolution of massive stars to core collapse. New treatments of radiation-dominated envelopes and improved solutions to stellar structure and composition equations have enhanced computational speed on multi-core processors. The MESA Software Development Kit (SDK) provides a unified build environment, and community tools enable rapid visualization of MESA results. The paper describes new capabilities in modeling giant planets, asteroseismology, and the evolution of massive stars, along with updates to physics modules, numerical methods, and visualization tools. MESA now includes detailed modeling of inert cores, irradiation effects, and surface heating, with applications to exoplanets and low-mass stars. The software has been validated against observational data and is used for a wide range of astrophysical studies.