PASADENA, Calif. — From “The Sopranos” and “Sex and the City” to “Big Little Lies” and “Game of Thrones,” one thing has been true at HBO: Original scripted programming airs on Sunday nights. There was even once a marketing slogan, “Sunday is … HBO.”

That’s about to change.

With HBO’s programming slate growing and the battle between networks and streaming services getting only more intense, the network will soon start shifting some original scripted series to Monday nights.

The prime-time expansion will begin with the limited series “Chernobyl,” scheduled to premiere in May. Other shows appearing on Monday nights during the rest of the year include the final season of the drama “The Deuce,” a limited series about Catherine the Great starring Helen Mirren and a new series adapted from Philip Pullman’s His Dark Materials books. There will be two hours of prime-time scripted series on HBO most Monday nights.

The reason, said Casey Bloys, the network’s president of programming, is simple.

“There’s obviously only so many Sundays in a year,” he said in an interview.