The paper significantly updates the open-source software MESA (Modules for Experiments in Stellar Astrophysics) to enhance its capabilities in modeling stellar evolution, pulsations, and explosions. Key advancements include: 1. **Binary Systems**: MESA now can simulate interacting pairs of differentially rotating stars undergoing mass and angular momentum transfer, significantly improving the modeling of binary evolution. New features allow for the accurate simulation of advanced burning stages needed to construct supernova progenitor models. 2. **Pulsations**: The coupling with the GYRE non-adiabatic pulsation software enables detailed exploration of instability strips for massive stars, accelerating the use of asteroseismic data in astrophysical studies. 3. **Implicit Hydrodynamics**: Implicit hydrodynamics with shocks can now be treated, enabling the modeling of the entire lifecycle of massive stars from pre-main sequence evolution to core collapse and nucleosynthesis from the resulting explosion. 4. **Advanced Burning and X-ray Bursts**: Large, in situ reaction networks allow for more accurate simulations of advanced burning stages and X-ray bursts. 5. **Mass Accretion**: Improved treatments of mass accretion provide more accurate and robust near-surface profiles, enhancing the modeling of accretion-induced collapse of massive white dwarfs. 6. **Weak Reactions**: On-the-fly calculation of weak reaction rates allows for better simulation of processes like the Urca process and accretion-induced collapse. 7. **Chemical Diffusion**: Improvements in particle diffusion methods, including radiative levitation, allow for more accurate simulations of heavy element distribution in hot stars. 8. **Software Infrastructure**: Bit-for-bit consistency across supported platforms ensures reliable and reproducible results. The paper also discusses the challenges and future improvements in these areas, emphasizing the ongoing development and future enhancements to MESA.The paper significantly updates the open-source software MESA (Modules for Experiments in Stellar Astrophysics) to enhance its capabilities in modeling stellar evolution, pulsations, and explosions. Key advancements include: 1. **Binary Systems**: MESA now can simulate interacting pairs of differentially rotating stars undergoing mass and angular momentum transfer, significantly improving the modeling of binary evolution. New features allow for the accurate simulation of advanced burning stages needed to construct supernova progenitor models. 2. **Pulsations**: The coupling with the GYRE non-adiabatic pulsation software enables detailed exploration of instability strips for massive stars, accelerating the use of asteroseismic data in astrophysical studies. 3. **Implicit Hydrodynamics**: Implicit hydrodynamics with shocks can now be treated, enabling the modeling of the entire lifecycle of massive stars from pre-main sequence evolution to core collapse and nucleosynthesis from the resulting explosion. 4. **Advanced Burning and X-ray Bursts**: Large, in situ reaction networks allow for more accurate simulations of advanced burning stages and X-ray bursts. 5. **Mass Accretion**: Improved treatments of mass accretion provide more accurate and robust near-surface profiles, enhancing the modeling of accretion-induced collapse of massive white dwarfs. 6. **Weak Reactions**: On-the-fly calculation of weak reaction rates allows for better simulation of processes like the Urca process and accretion-induced collapse. 7. **Chemical Diffusion**: Improvements in particle diffusion methods, including radiative levitation, allow for more accurate simulations of heavy element distribution in hot stars. 8. **Software Infrastructure**: Bit-for-bit consistency across supported platforms ensures reliable and reproducible results. The paper also discusses the challenges and future improvements in these areas, emphasizing the ongoing development and future enhancements to MESA.