Zelensky is expected to hold a series of bilateral meetings during the summit, which will be the last gathering in this format before U.S. President-elect Donald Trump takes office on Jan. 20."It's clear that a new chapter starts for Europe and the entire world just 11 days from now, when we have to cooperate even more, rely on each other even more, and achieve greater results together," Zelensky said in his opening address alongside outgoing U.S. Defense Secretary Lloyd Austin.Trump's imminent return to the White House has caused concern about the future of U.S. support for Ukraine, as the president-elect has often criticized the Biden administration's assistance provided to Kyiv.The U.S. is expected to unveil a $500 million aid package for Ukraine at the meeting, the last military aid tranche provided by the Biden administration.