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On July 9, 2025, the U.S. Department of Energy (DOE), Office of Science, Office of High Energy Physics and the U.S. National Science Foundation (NSF) issued a statement informing the CMB-S4 Project that “DOE and NSF have jointly decided that they can no longer support the CMB-S4 Project.” The CMB-S4 Project is proceeding with an orderly shutdown of the project, documenting the technical advances, survey simulations and instrumentation designs created by the project, and preserving access to the extensive document archive. The CMB-S4 Science Collaboration, which is an independent organization, is working to develop plans to best support the community.
The entire DOE and NSF Statement on the CMB-S4 Project reads:
Scientific research using data from the Cosmic Microwave Background (CMB) continues to be a priority for the DOE, Office of Science, Office of High Energy Physics, and the U.S. National Science Foundation, providing crucial information on the fundamental nature of matter and energy in the universe.
As recommended by P5 and Astro2020, DOE and NSF have been partnering on funding the design and development of a proposed next generation project, CMB-S4, with precision instrumentation at two sites, the South Pole and the Atacama Desert in Chile, dedicated to detecting primordial gravitational waves that would confirm the model of the Universe with a Big Bang followed by a period of rapid Inflation.
DOE and NSF have jointly decided that they can no longer support the CMB-S4 Project. DOE and NSF will continue to partner with the CMB science community to explore the potential science that can be achieved with limited upgrades to existing experiments to further this important U.S.-led research.