HBO Max -- Warner Media's answer to Netflix, Disney+ and the like -- is catching on quickly.

The company doubled the number of new HBO Max subscribers last quarter and now has 38 million HBO and HBO Max customers. That's enough to surpass HBO's year-end target.

AT&T, which owns CNN parent company Warner Media and the fledgling streaming platform, said Thursday that the "growth and scale of HBO Max continues to show strong momentum," after adding 8.6 million new customers over the past three months.

Still, most of HBO Max customers aren't completely new. The number of total HBO and HBO Max subscribers in the United States grew by fewer than 2 million in the past quarter.

That means the bulk of its new customers are HBO customers changing to HBO Max -- which was already available to them. Between HBO and HBO Max, the two services combined have a total 57 million subscribers globally.

With its reach limited to the United States, the five-month old platform trails its competitors in terms of subscription numbers.

Disney+ has about 60 million members and Netflix (NFLX) has nearly 195.2 million subscribers. HBO Max plans to launch an ad-supported service next year and likely expand globally.

It's also still not available on Roku (ROKU) and Amazon (AMZN) Fire TV devices — two of the most popular devices that consumers use to watch streaming services.

Ultimately, AT&T (T) aims for HBO Max to have 50 million US subscribers by 2025.

In its third-quarter earnings released Thursday, AT&T's revenue of $42.3 billion in revenue came in slightly above analysts' expectations.

The company added 645,000 new phone subscribers, but had a net loss of 590,000 subscribers to its premium TV services, like DirecTV.

"We delivered a solid quarter with good subscriber momentum in our market focus areas of connectivity and software-based entertainment," said CEO John Stankey.

Shares climbed more than 1.5% in premarket trading.