Gary Levin

USA TODAY

Game of Thrones ends its sixth deadly season Sunday (9 ET/PT), and while fans haven't loved every battle, they're still watching HBO's biggest hit in record numbers.

The fantasy series marks the network's first to run six years while consistently building its audience, HBO says, citing Nielsen and streaming data provided exclusively to USA TODAY. Through June 17, the series has averaged 23.3 million viewers across all platforms, up 15% from last year.

The breakdown: Sunday premiere ratings are up 6%, to 7.3 million, while overall TV and on-demand viewership is up 4%. But viewing on HBO Now and HBO Go digital platforms skyrocketed 70% over last season, to about 2.5 million streams, reflecting growth in HBO Now subscriptions since the app's launch in April 2015.

HBO Go, introduced in 2010, allows the premium cable network's 33 million subscribers to watch series and movies on mobile devices or away from home. HBO Now, added just before Thrones' fifth-season premiere, gives non-subscribers access to HBO's library for $15 a month.

HBO says HBO Now had 800,000 subscribers as of Jan. 1, a figure that has presumably climbed since then. And the 2.5 million average weekly viewership on digital platforms — aimed squarely at the series' young male fan base — is based on a combination of view counts and time spent watching, though multiple viewers on a single device aren't counted. .

Thrones' Sunday comedy companions are also up, though not nearly as sharply: Silicon Valley, averaging 6.4 million viewers, is up 4% this season, but while HBO Now and HBO Go viewership is up 37% from last season, TV ratings dipped 4%. And Veep, averaging 4.4 million viewers, is up 6% overall; TV ratings edged up 1%, but its digital audience climbed 40%.

The lesson? Contrary to fears in some circles, HBO Now "doesn't cannibalize anything on the (TV) network," says CEO Richard Plepler. "It simply expands the audience's opportunity to watch our programs. It's all about expanding the pie."

Later this summer, HBO Now will become home to more original content not shown on TV, including bonus material from Bill Simmons, whose sports and pop-culture talk show Any Given Wednesday premiered this week. And this fall, former Daily Show host Jon Stewart will launch a series of digital shorts on the service, refreshed several times a week.

Aside from Netflix, Hulu and Amazon, traditional broadcast and cable networks are experimenting with original series to drive subscriptions to their apps: CBS All Access, which costs $5.99 a month, will be the exclusive home to a new Star Trek series due in January, and a spinoff of The Good Wife, starring Christine Baranski, later next year.