According to this article, Valve abandoned the episodic model shortly after Episode 2 and began work on a full sequel, as it’s considered a rumor I ask if it’s true or not. That’s for you to decide.
https://www.nowgamer.com/news/6322/half-life-3-new-rumours-hot-up-debunked-by-valve
EDIT: Doug Lombardi sent out an email regarding this as fake, could just be a cover but that’s not likely.