From the Introduction: "The New START Treaty [Strategic Arms Reduction Treaty] would have expired on February 5, 2021, unless the United States and Russia agreed to extend it for up to five years. On January 21, 2021, the Biden Administration announced that it would seek a five-year extension of New START, leading to an exchange of diplomatic notes and the formal extension of the treaty on February 3, 2021. The State Department noted that the extension was a first step that would provide 'the stability and predictability [needed] to enhance and expand discussions with Russia and China.' The United States and Russia held several meetings during 2020 to discuss New START extension and a framework for a future agreement, but did not reach an agreement. In April 2019, President Trump had called for expanded arms control efforts with Russia and China, both to capture all types of Russian weapons and to bring China into the process. In December 2019, Russian President Vladimir Putin had indicated that he would extend New START for five years, without preconditions; Russian officials also noted that the countries could address other weapons systems in separate talks after extending New START."
CRS Insight, IN11520
Congressional Research Service: https://crsreports.congress.gov/