Facebook today announced that it will add a subscribe button to the Facebook Mentions livestreaming app, allowing fans to tune in right as people are beginning to broadcast a new stream.

Mentions opened up to Facebook users with verified profiles in August. People broadcasting with the app include U.S. House Speaker John Boehner, journalist Jorge Ramos, musician Alicia Keys, and tennis player Serena Williams.

The actor Vin Diesel has reached more than 1 million live viewers with the app, product managers Vadim Lavrusik and Peter Yang wrote in a blog post today. U.S. presidential candidate Donald Trump and actors Kevin Hart and Ian Somerhalder have all gotten more than 200,000 people to watch their live streams, Lavrusik and Yang wrote.

And the app isn’t just showing content from the U.S., where Facebook is based.

“More than 60 percent of broadcasters are from countries outside the U.S.,” Lavrusik and Yang wrote.

Twitter got into the live streaming business by acquiring Periscope earlier this year. Just before that, live streaming app Meerkat was cut off from the Twitter application programming interface (API).

Facebook Mentions is not available for Android devices.