At the top of his State of the Union remarks, President Biden acknowledged the changes that came with the 118th Congress, including offering congratulations to McCarthy, the newly elected Republican Speaker of the House.

"I don't want to ruin your reputation, but I look forward to working with you," Biden said after turning around to shake the Republican's hand -- a gesture of goodwill ahead of what is likely to be a two-year period of legislative debate and conflict between Biden and McCarthy's parties.

The president then congratulated the new leader of the House Democrats and the first Black House minority leader in history, Hakeem Jeffries.

Biden then nodded to the longest serving Senate leader in history, Mitch McConnell, as well as Chuck Schumer's latest term as Senate majority leader -- "this time with an even bigger majority."

Biden ended his introduction by lauding former Speaker Nancy Pelosi, someone who he said "will be considered the greatest speaker in the history of this country."

President Biden entered the chamber just after 9 p.m. ET to expected applause from the attendees.

He shook the hands of many lawmakers as he made his way to the podium.

Members began steadily streaming into the House chamber on Tuesday with Vice President Kamala Harris around 8:30 p.m. ET, including some former lawmakers who are also using floor privileges.

The realities of a divided government are on full display -- little conversation between Democrats and Republicans across the aisle on the House floor.

The vice president has been making small talk with House Speaker McCarthy -- overheard on the mics saying it's a "packed house."

Former Rep. Rodney Davis, R-Ill., was seen joking to Rep. Joe Wilson, R-S.C.-- infamous for shouting "you lie!" at former President Barack Obama during a joint address of Congress -- to "sit down, sit down Joe."

Former Department of Housing and Urban Development Secretary Ben Carson is at the speech as one of the only former Trump officials spotted thus far.

Newly independent Arizona Sen. Kyrsten Sinema made her way in, standing next to GOP Utah Sen. Mitt Romney and was then speaking with Republican Senate Minority Leader Mitch McConnell.

For some, the most coveted seats appear to be along the aisle. That's where embattled Rep. George Santos chose to sit, in position to shake the president's hand as he enters and exits the chamber. Santos still has time to switch seats.

Some of the president's fiercest critics are also along the aisle: Republican Reps. Matt Gaetz and Lauren Boebert.

Rep. Marjorie Taylor Greene was carrying around a white balloon through the halls of Congress for much of the day to mock the administration's handling of the suspected Chinese spy balloon -- but decided to not bring it into the chamber.

Speaker McCarthy's guest, Enes Freedom, New York City Mayor Eric Adams, Cabinet secretaries Pete Buttigieg and Jennifer Granholm and pollster Frank Luntz have also filed into the room.

-ABC News Senior Congressional Correspondent Rachel Scott, Katherine Faulders and John Parkinson

A moment between embattled Rep. George Santos and Sen. Mitt Romney ahead of Biden’s speech is catching attention on social media.

The two Republicans appeared to be exchanging insults on the House floor before the president's arrival.

"You should be embarrassed ... you shouldn't be here," Romney seemingly said to Santos, who was sitting off the center aisle of the chamber.

The two went back and forth again before Romney walked away.

On another feed, Santos can be seen repeatedly saying "what an a------" to his seat mate, Rep. Thomas Massie, R-Ky., in apparent reference to Romney.

-ABC News' Justin Fishel and Ben Siegel

The opposition response to the State of the Union has been around for more than half a century, but in modern times the opposition party has often used it to showcase a new, high-profile figure. It's no different this year, as Republicans were represented by Arkansas Gov. Sarah Huckabee Sanders, who served as a press secretary in the Trump White House.

Sanders just won her new office in November, making her the first woman governor in Arkansas's history. This puts her right at home with many first-term governors, senators and representatives who've given a response speech in recent years. Previous orators include Democratic Gov. Tim Kaine of Virginia in 2006, Republican Sen. Marco Rubio of Florida in 2013, Republican Sen. Joni Ernst of Iowa in 2015 and Democratic Gov. Gretchen Whitmer of Michigan in 2020.

And with the proliferation of response speeches in different languages and from various party factions, even more fresh faces are in the limelight this year. First-term GOP Rep. Juan Ciscomani of Arizona gave the Spanish-language response for his party, while first-term Democratic Rep. Delia Ramirez of Illinois offered the Working Families Party's response.

-FiveThirtyEight's Geoffrey Skelley