That figure is still fairly small when compared to Netflix's numbers (which reportedly sit at around 58 million subscribers as of writing), but it's still a significant milestone, and it means Hulu is doing something right.
It's tough to pin down precisely what that something might be, but there are plenty of possibilities. For example, as some of Netflix's long-time users will know, Hulu has snaked away several show contracts from its competitor over time (such as popular adult animated comedy Bob's Burgers).
By doing so, Hulu positions itself as the sole provider of that content, forcing even the most loyal Netflix users to make the switch (or subscribe to both platforms simultaneously) to keep up with their favorite shows cable-free.
Of course, Hulu's recent push for more original content has also likely been a factor behind the platform's growth. Like Netflix, Hulu recognizes that to acquire and retain subscribers long term, it needs shows and movies viewers can never get anywhere else - Netflix has House of Cards, and Hulu has The Handmaid's Tale. Both shows have been massive critical successes, and likely draw in new subscribers on a regular basis.
Moving forward, according to Variety, Hulu will be focusing on expanding its international reach and launching new original content offerings to better compete with other major players in the video streaming industry.