Diablo 4 wasn't announced at Blizzcon 2018 and Blizzard denied that an announcement had ever been planned. However there are indications that new Diablo games are gestating somewhere deep in Blizzard's secretive development vaults. The Prime Evil has a knack for coming back to terrorise Sanctuary.
In August Blizzard explicitly said that there are 'multiple Diablo projects in the works'. Community manager Brandy "Nevalistis" Camel made a statement at the start of Diablo 3: Season 14.
"The forges here at Blizzard are burning hot. And we have multiple Diablo projects in the works. Some of them are going to take longer than others. But we may have some things to show you later this year. We hope you stay tuned, while we work to bring these Diablo experiences to life. None of this would be possible without the support that you have shown us for over 20 years.
"So whether you first joined us in Diablo 3 or you are a seasoned veteran, thanks you. Diablo is, and always will be, part of Blizzard's identity, and we can't wait for the future."
The statement was accompanied by a video called 'The Future of Diablo'.
The "some things to show you later this year" turned out to be a mobile game called Diablo Immortal, which wasn't received well by core Blizzard fans watching the opening ceremony at Blizzcon. Blizzard has reiterated since that more Diablo is in production, but the terms "projects" and "experiences" could mean anything, from a proper big new Diablo game to, who knows, a ten minute VR demo, or maybe even a TV series.
In February 2019 during an Activision Blizzard earnings call the publisher laid off hundreds of employees, but reiterated its commitment to Blizzard's big series. In the same earnings call COO Coddy Johnson suggested that "Diablo's development headcount will grow substantially as the teams work on several projects underway for the franchise". There's nothing imminent, however, as no major new games are coming from Blizzard in 2019.
These are the suggestions that point towards Diablo 4's possible existence
There are some hints that Blizzard are working on something very traditional. In June 2018 Blizzard started recruiting for some telling roles. "We are working on a new, unannounced Diablo project. Are you a skilled Dungeon Artist? Come work with us, and together we will build something exceptional," read one post.
The dungeon artist's responsibilities include building "atmospheric dungeons" as you'd expect, "with a focus on composition, detail and mood, while ensuring that the gameplay space is readable."
Blizzard was also looking for a technical artist to "help the environment and prop teams define, create, maintain and streamline the modelling and world-building pipeline and processes to bring to life the world of Sanctuary."
The good news: these roles are unlikely to be related to Diablo Immortal. It sounds like much of Diablo Immortal's development is in the hands of Tencent, and Immortal looks too far along to need new artists and designers. These roles are likely to be supporting a proper Blizzard joint. Bad news: if Blizzard is recruiting in 2018 it's unlikely we'll see the fruits of that work for a few years yet.
Going further back, to 2016, Blizzard was searching for a game director to "lead the Diablo series into the future." The hire would be "the vision holder for the franchise, setting the creative goals for the team". The role required "an awareness of global player behaviour and customs to ensure that design decisions are relevant for international regions", which certainly plays into the announcement of Diablo Immortal.
I wouldn't make any guesses about a Diablo 4 release date yet, then. But considering the snippets of news and rumours we've heard in recent years it seems reasonable to hope for a new Diablo action RPG at some stage, even though it could be quite a wait still. Let's spend that time speculating about what Blizzard could do next with the Diablo series.