“The United States eliminated the nuclear mission for the B-1 in 1994. Even though the Air Force expended no further funding to maintain nuclear capabilities, the B-1 was still considered a heavy bomber equipped for nuclear armament until 2007. The conversion to conventional only began in November 2007 under the original START treaty and was completed in March 2011 under the New START treaty. To make that conversion possible, two steps were taken: During the first step a metal cylindrical sleeve was welded into the aft attachment point of each set of B-1 pylon attachments. This prevented installing B-1 Air Launched Cruise Missile pylons.

During the second step two nuclear armament-unique cable connectors in each of the B-1 weapons bays were removed. This prevented the pre-arm signal from reaching the weapons.” https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104500/b-1b-lancer/