In 2021, California launched the Universal Prekindergarten (UPK) program (AB 130), requiring public schools with kindergarten to provide free, high-quality, inclusive pre-kindergarten to all four-year-olds regardless of birth date. Starting in 2022, it increased the original age-eligibility for Transitional Kindergarten (TK)--students turning five in the fall--to include younger four-year-olds incrementally. This mandate comes to completion in the 2025-26 school year, which is fast approaching. To ascertain how well expansion is working, the authors examined enrollment data and interviewed ten districts. This Policy Brief covers a few of the key findings.