Licensing
Build and ship freely. We only share in the hits.
Open Terrain Engine is pre-release and in active development — not yet generally available. This page describes the licensing model that will apply once versions are published; nothing here implies a finished or downloadable product. The model is simple: read and modify the source, then build, run, and ship your own games commercially at no charge — for every title until it passes US $1,000,000 in cumulative lifetime gross revenue. Above that, a single title needs a commercial (royalty) license, and every released version automatically becomes open source (Apache-2.0) four years after it's first published. This is a summary, not legal advice — the published LICENSE (BSL 1.1) is the binding text and governs if anything here conflicts.
Pre-release — the model below applies once versions are published
At a glance
| You want to… | Allowed? |
|---|---|
| Read, study, modify, and redistribute the engine sourceThe BSL grants the right to copy, modify, create derivative works, redistribute, and make non-production use — the engine is not a black box. | Yes |
| Build a game and sell it — free under $1M lifetime gross per title (ship the runtime embedded inside it)Covered by the Additional Use Grant, including commercial use and distributing the runtime portions of the engine embedded within your game. | Yes |
| Use it at a company or studio — internally and on client game projectsBuilding games and applications for clients or internally is fine, subject to the same per-title $1M threshold. | Yes |
| Use a released version once it reaches its 4-year Change DateFour years after a version is first publicly available it auto-converts to Apache-2.0: fully open source, royalty-free, unrestricted (that version only). | Yes |
| Keep selling a title after it passes $1,000,000 lifetime grossThat title needs a commercial license — an indicative ~5% royalty on revenue above the threshold; exact rate set in the commercial terms. | Royalty |
| Resell, re-host, sublicense, or re-brand the engine itself — or ship a competing engine/SDK from a forkNot permitted by the Additional Use Grant. Sell the milk, not the cow — for a commercial-engine arrangement, contact us. | No |
| Use the “Open Terrain Engine” / “Open Terrain Studios” names or logos to brand your productThese are trademarks of Open Terrain Studios LLC; the BSL grants no trademark rights. | No |
Source-available / Fair Source — not open source
Open Terrain Engine is licensed under the Business Source License 1.1 (BSL 1.1). Once released, the full source is published so you can read it, learn from it, modify it, and build real games with it — but the BSL is not an OSI-approved open-source license, and we never call it that. We describe it as source-available / Fair Source. The base license grants the right to copy, modify, create derivative works, redistribute, and make non-production use of the engine; the Additional Use Grant is what additionally permits commercial production use (below). The Licensor is Open Terrain Studios LLC; the engine is © 2026 Open Terrain Studios LLC.
Free to build and ship — including commercially
The Additional Use Grant lets you develop, build, run, and distribute your own games and applications with the engine — including for commercial purposes, and including distributing the runtime portions of the engine embedded inside your game — free of charge for each title whose cumulative lifetime gross revenue does not exceed US $1,000,000. The $1,000,000-per-title threshold is a published, firm term of the license, not an estimate. Most projects never reach it and pay nothing.
A royalty only on a genuine hit
For any single title whose cumulative lifetime gross revenue passes US $1,000,000, continued production use of that title requires a commercial (royalty) license. The economics are modeled on Unreal-style terms: an indicative ~5% royalty on revenue above the threshold. The ~5% rate and the precise definition of “gross revenue” are indicative only — they are set in the commercial terms, not fixed on this page. The $1,000,000 threshold itself is firm and published.
The threshold is per title, over that title's lifetime
The $1,000,000 is measured per individual title, across that title's whole lifetime — each game you ship gets its own $1,000,000 allowance. It does not aggregate across your studio's catalog. A modest game and a breakout hit from the same studio are tracked independently: only the title that crosses $1,000,000 triggers a commercial license, and only for that title.
Every version becomes Apache-2.0 — time-delayed open source
The BSL is time-delayed open source. Each released version of the engine automatically converts to the Apache License 2.0 on its Change Date — four years after that version is first made publicly available (the Change Date may vary per version). After that date the version is fully open source under Apache-2.0, with no restrictions and no royalty. The license also applies separately for each version, so the restrictions here are temporary and per-version: the newest releases are Fair Source while older releases roll into permissive open source on schedule.
You can ship games with it — you can't ship it as an engine
The Additional Use Grant does not permit you to offer, distribute, host, sublicense, or resell the engine itself (or any fork, modified version, or substantial portion of it) to third parties as a game engine, development framework, development tool, SDK, or hosted/managed service — whether or not for a fee — nor to ship a competing engine built from it. The model is “sell the milk, not the cow”: make and sell your games freely, but the engine itself stays with the studio. Two compliance notes: if you redistribute the engine source you must conspicuously include the LICENSE with it, and using the engine in violation of the license automatically terminates your rights to the current and all other versions. Separately, every dependency the engine uses is permissive (MIT / Apache-2.0 / BSD / Zlib / public-domain) with zero copyleft, so adopting it doesn't pull copyleft obligations into your game; and the BSL grants no trademark rights.
The binding terms
This page is a plain-language summary. The authoritative text lives in the public engine repository — the LICENSE governs if anything here conflicts.
FAQ
Is this open source?
No. Open Terrain Engine is source-available / Fair Source under the Business Source License 1.1 — once released you can read, study, modify, and redistribute the source, but it is not an OSI-approved open-source license. That said, each released version does become open source under Apache-2.0 four years after it is first made publicly available — see below.
Do I owe anything to ship a game made with it?
Not until a single title passes US $1,000,000 in cumulative lifetime gross revenue. Below that, building and selling your game — including embedding the runtime portions of the engine inside it — is covered by the Additional Use Grant at no charge. Above it, that title needs a commercial (royalty) license, with an indicative ~5% royalty on revenue above the threshold. (Separate from this license, a storefront like Steam has its own terms.)
Is the threshold per game or for my whole studio?
Per title. Each game has its own US $1,000,000 lifetime-gross threshold, measured over that title's lifetime, and it does not aggregate across your catalog. Only the specific title that crosses $1,000,000 needs a commercial license — and only that title. One breakout hit doesn't change the status of your other games.
What is the royalty above $1M, and is it final?
Above the $1,000,000-per-title threshold, that title needs a commercial license — an indicative ~5% royalty on revenue above the threshold, modeled on Unreal-style economics. Treat ~5% as indicative: the exact rate and the precise definition of “gross revenue” are set in the commercial terms, not finalized here. The $1,000,000 threshold itself and the four-year Apache-2.0 conversion are firm, published terms of the license.
Will my version ever become fully open?
Yes. Each released version automatically converts to the Apache License 2.0 on its Change Date — four years after that version is first made publicly available (the Change Date may vary per version). After that it is unrestricted and royalty-free. Newer releases stay under the BSL until their own four-year clock runs out. (The engine is still pre-release, so no version has shipped or converted yet — this is how it will work once versions are published.)
Can I use it at work or for a client project?
Yes. Building games and applications, including for clients and internally at a company, is permitted — subject to the same per-title $1,000,000 threshold. The line that needs a commercial license is offering the engine itself to a client as an engine, framework, SDK, dev tool, or hosted service. Building the client's game with it is fine; handing them the engine as a product is not.
What exactly can't I do — and is BSL the same as the BSD license?
You can't offer, host, sublicense, or resell the engine itself (or a fork, modified version, or substantial portion) as an engine, framework, SDK, dev tool, or hosted service; you can't ship a competing engine built from it; you can't keep selling a title past $1,000,000 lifetime gross without a commercial license; and you can't use our trademarks or logos to brand your product. If you redistribute the engine source you must conspicuously include the LICENSE, and using the engine in violation of the license terminates your rights to the current and all other versions. And no — BSL is not BSD: BSD is a permissive open-source license; the Business Source License (BSL) is a source-available license with the per-title revenue threshold and time-delayed-Apache-2.0 conversion described above.
Will it pull copyleft into my game, and where are the binding terms?
No copyleft: every dependency the engine uses is permissive (MIT / Apache-2.0 / BSD / Zlib / public-domain), enforced in CI, so adopting it doesn't pull copyleft obligations into your title. The binding text is the published LICENSE (Business Source License 1.1), with LICENSING.md as the plain-English companion — both in the public engine repository (linked above). This page is a summary; if anything here conflicts with the LICENSE, the LICENSE governs.
Summary — not legal advice. This page is an informational summary to help you understand the licensing model — it is not the license and not legal advice. The binding terms are in the engine's LICENSE (Business Source License 1.1), with LICENSING.md as the plain-English companion, both published in the public engine repository; if anything here conflicts with the LICENSE, the LICENSE governs. The US $1,000,000-per-title threshold and the automatic conversion to Apache-2.0 four years after each version is first publicly available (the Change Date may vary per version) are published terms of the license. The ~5% royalty rate and the precise definition of “gross revenue” are indicative only and are set in the commercial license terms, which are still being finalized with counsel. The engine is pre-release and in active development — not yet generally available. “Open Terrain Engine” and “Open Terrain Studios” are trademarks of Open Terrain Studios LLC; the license grants no trademark rights. © 2026 Open Terrain Studios LLC. For a title past the $1M threshold, commercial-engine licensing, or anything the Additional Use Grant doesn't cover: licensing@openterrain.studio.