Lindsay Colas, Brittney Griner's agent, said Griner "has carried herself with courage, grace and grit” and is expressing thanks to everyone who helped bring her home, including U.S. officials, the WNBA and the NBA.

Colas especially thanked President Joe Biden, who she said “kept his word."

“Also, to so many people around the world who raised their voices and stood with us - especially Black women, the LGBTQ+ community and civil rights leaders - thank you,” Colas said in a statement.

Colas said Griner will continue to advocate for other Americans held abroad and called people out by name, including Paul Whelan, who remains imprisoned in Russia, and Americans who are in Iran, Venezuela, China, Syria, Mali and Rwanda.

“Our commitment to President Biden and to the families of Americans who are being held hostage and wrongfully detained – especially Elizabeth and David Whelan, on behalf of their brother Paul Whelan, who remains in Russia and whose continued detention weighs heavily on our hearts – is to continue our work in the movement to bring them home,” Colas said.

The prisoner swap that resulted in Brittney Griner’s release has been in the works since at least Nov. 29, when the U.S. government requested the removal of Viktor Bout from USP Marion in Marion, Illinois, according to a court document unsealed Thursday.

The document, signed by George Turner, assistant United States attorney from the Southern District of New York, requested the Bureau of Prisons allow U.S. Marshals to take custody of Bout sometime between Dec. 2 and Dec. 16.

The move was “based on the significant foreign policy interests of the United States,” the document said, but did not mention Griner or a prisoner exchange.

The government expended significant resources and time to bring Bout to justice, but a source familiar with the prosecution of Bout said they recognized the "competing interests" that resulted in his release from U.S. custody.

Whether Bout represents a future threat, this source said that while Bout is not old he has been "out of the game," which would impede his ability to go back to his former operations. However, the source called Bout a "shrewd operator" with "a lot of friends" in Russian military and intelligence circles.

-ABC News' Aaron Katersky

Elizabeth Whelan, the sister of ex-Marine Paul Whelan, the U.S. citizen being held in Russia as an alleged spy, told ABC News in an interview Thursday she is happy for Brittney Griner, but also frustrated Paul remains in custody.

"The Russians have been clear with all of these cases that they treat them all separately," Elizabeth Whelan told ABC News. "We try to bundle them together and get everybody out at once. We don't want to leave anyone behind. But that is not necessarily the way our opponents are dealing with this situation."

"We've always known that the Russians were treating Paul separately, and therefore, we always knew that there was a chance that this would happen, that Brittney would be released first," she continued.

U.S. officials said they wanted to exchange Viktor Bout for both Griner and Paul Whelan, but that Russian officials would not engage on both and said either Griner could be swapped for Bout or no one could be swapped.

"I think we need to start dealing with Russia as the entity that it actually is now and not the way we might want it to be," Elizabeth Whelan said. "They talk about Paul being a spy, but they're the ones who set Paul up and created this spy story that is sort of based in a fairy tale [that] has to be undermined. We have to find a way around that."

President Joe Biden delivered the good news about Brittney Griner's release in person directly to her wife, Cherelle, at the White House Thursday morning, according to press secretary Karine Jean-Pierre.

"Cherelle had been invited to the White House for a meeting with the national security adviser Jake Sullivan. When she arrived, she was welcomed into the Oval Office by President Biden, who personally delivered the news that Brittney would be returning home today," Jean-Pierre said.

ABC News' Mary Bruce pressed the White House on any plans Biden has to meet with Griner upon her return to the United States, but Jean-Pierre didn’t have any guidance.

"I don't have anything to preview at this time. Our efforts right now, our focus, is to get her home safely and to get her back to her family, to her team, to her loved ones, and give her all the necessary tools she will need to reengage, to come back to the U.S. in the way that she chooses, right?" Jean-Pierre said.

-ABC News' Molly Nagle