It was called "Xtra News" and it was first. I don't recall that KABC ever had an all-news format. They ran long blocks of news in the morning and afternoon, but was otherwise talk shows- like KGO until recently,
Rumor had it that Gordon McLendon did all news because he heard the world's original all news station on a vacation to Pre-Castro Cuba in the late 50's. Radio Reloj (Radio Clock) and it's eventual Reloj Nacional network went on the air in 1948 with all news.