While there are general guidelines for handling no-cost extensions, some sponsors have specific procedures. Please see the links below for guidance regarding those sponsors with specific requirements or processes.
Air Force Office of Scientific Research (AFOSR)
National Aeronautics and Space Administration (NASA)
National Institutes of Health (NIH)
National Science Foundation (NSF)
National Endowment for the Humanities (NEH)
Space Telescope Science Institute (STScI)
U.S. Dept. of Agriculture (USDA)
Foundations