Russian officials allowed Taylor Dudley, a 35-year-old U.S. citizen to cross the Polish border. Mr. Dudley had been held for nine months, the spokesman said, though his case was largely unknown to people outside the U.S. government, his family and its advocates.

Mr. Dudley was greeted in Poland by an official from the U.S. Embassy in Warsaw and Bill Richardson, a former New Mexico congressman and governor who specializes in negotiating the freedom of Americans detained overseas.

Mr. Dudley was backpacking in Europe and had traveled to Poland to attend a music festival, according to the spokesman, Jonathan Franks. He said Mr. Dudley “at some point crossed the Russian border” into Kaliningrad. It remained unclear on what charges he was being held.

It was not clear what, if anything, the U.S. might have offered Russia in return for Mr. Dudley’s freedom, which came less than five weeks after Russia’s release of WNBA star Brittney Griner in a prisoner swap with the Biden administration. A spokesman for Mr. Richardson told CNN, which first reported the news, that no exchange had been made by the United States.

[Maybe we sent them Alexanda Kotey. I’m (mostly) kidding about that, but how many more Americans are being held by Russia that we don’t know about? — Ed]