Update April 27th per todays press release:

WarnerMedia have today confirmed HBO Max availability for exisiting Apple HBO Now customers as-well as full integration with the Apple TV App.

At launch, customers will be able to access HBO Max on iPhone, iPad, iPod touch, Apple TV 4K and Apple TV HD. Customers with second and third generation Apple TV models can stream HBO Max content from their iPhone or iPad to their TV with AirPlay. Existing HBO NOW customers who are billed through the App Store and HBO subscribers through Apple TV channels can log in and access the HBO Max app at no additional charge. New HBO Max customers will be able to subscribe directly in the app using in-app purchase.

Original April 21st article:

HBO Max, Warner Media's forthcoming streaming service will launch on May 27th for $15 per month. With over 100,000 hours of premium content from Warner Bros library of Movies and TV shows and a slew of original content ready to stream on day one, consider my interest peaked.

Per WarnerMedia's press release:

All of HBO’s premium originals such as Westworld, Big Little Lies, Game of Thrones, Sex and the City, Veep, The Wire, Curb Your Enthusiasm, Insecure, Succession, Watchmen, Barry, Euphoria, The Jinx, The Sopranos and more.

Highlights of the extensive WarnerMedia portfolio of programming and acquisitions that will be available on day one include the libraries of Friends; The Big Bang Theory; (new) Doctor Who; Rick and Morty; The Boondocks; The Bachelor; Sesame Street; The Fresh Prince of Bel-Air; CW shows such as Batwoman, Nancy Drew, and Katy Keene; the first season of DC’s Doom Patrol; The O.C.; Pretty Little Liars; the CNN catalogue of Anthony Bourdain: Parts Unknown; and much more. Soon after, the platform offering will continue to grow adding the libraries of South Park, Gossip Girl, The West Wing, and more within the first year of launch.

Available films will include Casablanca, The Wizard of Oz, The Matrix, The Goonies, When Harry Met Sally, The Lord of the Rings, Citizen Kane, Gremlins, and the Lego movies, along with every DC film from the last decade, including Wonder Woman, Justice League, and every Batman and Superman movie from the last 40 years.

Max Originals to look out for on launch include new 'Looney Tunes Cartoons’, scripted comedy 'Love Life ’ starring Anna Kendrick and 'The Not-Too-Late-Show with Elmo’.

Most notably, high profile Russell Simmons accuser documentary ‘Off The Record’ will be available to stream on HBO Max at launch. The once Apple TV+ bound project was dropped in January by the films former-executive producer Oprah Winfrey following creative differences.

HBO Now subscribers will get access to HBO Max at no additional cost, if your subscription is “billed directly through HBO.” If your HBO Now subscription is billed through a third party - including Apple Channels - HBO have said that details will become available closer to launch, meaning negotiations are most likely ongoing.

HBO subscribers through AT&T TV or U-Verse TV will get HBO Max at no additional cost.