By Paul Sandle

LONDON Candy Crush Saga, the matching game played by millions on their commute, has reached $20 billion in revenue since its 2012 launch, maker King said, adding that it would soon release levels up to 15,000 for the most dedicated players.

First appearing on a website, it shifted to Facebook and then mobile, where it took off and has now been downloaded 5 billion times.

It pioneered the "freemium" model, in which the game is free but players can spend money to boost their performance or can watch ads to gain moves.

King President Tjodolf Sommestad said Candy Crush Saga and its other titles like Farm Heroes Saga showed that mobile games could have enduring appeal.

"We've proven to ourselves and to the industry that it is possible to reignite games that are years old and keep them relevant for a decade or longer, and break records even a decade in," Sommestad said in an interview.

Todd Green, Candy Crush general manager, said the game was constantly updated to make it more satisfying, from optimising the tiny bounce when candies land in the grid to adding new levels, including the 15,000 milestone.

Candy Crush has been the top-grossing franchise in U.S. app stores for the last six years, a fact Sommestad said underlined both the success of King's strategy and the challenge for new game developers.

"We do have an effort to build new games, but the bar is very high and it takes a lot to launch a new game nowadays," he said. "Candy Crush took us a few months to build but we added 10 years of development after that."

King has been owned since 2016 by Activision Blizzard, the U.S. company behind "Call of Duty" that has agreed a $69 billion takeover by Microsoft. King contributed $747 million in net revenue in the second quarter, 31% of Activision's total.

(Reporting by Paul Sandle; Editing by Bill Berkrot)