In a blog post, Improbable explains that the December 5 update to Unity's terms includes a clause, 2.4, that creates a change forcing all operation and development of SpatialOS games using Unity to cease.
Section 2.4 of Unity's software terms of service forbids streaming or broadcasting Unity software, including the Unity Runtime, if it's executed or simulated by a remote server and transmitted over any network to an end user device without a separate license from Unity. The answer probably lies in the "partnership" that both Unity and Improbable allude they were in the process of reaching, i.e. Unity likely wanted Improbable to pay up if they were going to be hosting the Unity Runtime on Improbable servers, but the two couldn't come to an agreement.
"Epic Games and Improbable would like to jointly reaffirm our commitment to giving game developers the best combination of engine and other technology backed by interoperable standards that work for everyone, while respecting developers' ability to choose partners and software components freely" Epic wrote in their own blog post. Worse, it has left some live and in-development games in legal limbo.
Unity is well-known as one of the most popular cross-platform game engines. Waleed Amer, lead developer at Arcane Reality and the upcoming indie title Overduty VR, noted that the terms of service change meant that the studio rewriting and converting to another engine would take several months or even a year, wasting valuable time and resource.
Bossa Studios' "Worlds Adrift" also uses both platforms, but said it's now "operating as normal".
But Improbable can't be certain what the real issue is until it discusses the matter in depth with Unity, something that company plans to continue doing.
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Business Insider has contacted Unity for comment.
Unity has since responded, saying Improbable's version of events is incorrect.
"We terminated our relationship with Improbable due to a failed negotiation with them after they violated our terms of service", said Ante.
Overnight, this is an action by Unity that has immediately done harm to projects across the industry, including those of extremely vulnerable or small scale developers and damaged major projects in development over many years. While the folks at Improbable also seemed unsure about this detail, Unity clarified in its blog post that SpatialOS projects that were live and in production would still be supported.
Ante said Unity informed Improbable in writing six months ago that they were in violation of the company's Terms of Service. But in a odd twist, Unity released a statement (via Game Informer) saying that what Improbable was saying wasn't the whole story: they knew about their violations months ago, and Unity only took action because of Improbable's inaction.
An Improbable spokesman told Business Insider that it was hard to estimate the potential financial impact on the startup, but added that the situation with Unity was "unique".
The change is a blow, but won't impact all games running on SpatialOS.