With this episode, Peter Scanavino and James Murtaugh have now been on all five of the NYC-based Law & Order shows.
TAPU stands for Threat Assessment and Protection Unit, also known as the Intelligence Unit, it is the NYPD's counter-terrorism unit and is responsible for gathering intelligence on threats to New York City and city employees, and providing protection to any area or person in danger of being attacked. This is the unit Elliot worked for in Italy before he transferred to the Organized Crime Taskforce, TAPU frequently works with the FBI, Homeland Security, INTERPOL and the law enforcement agencies of other countries who are threatened by the same terrorist groups as New York is.
Elliot calls Olivia at the end of the episode about what he's found about Sacha Lenski, but she ignores the calls. She is shown listening to the voicemail he left in the Law & Order: Special Victims Unit (1999) episode Trick-Rolled at the Moulin (2021).