How Dual Licensing Helps Open Source Projects Stay Sustainable

Open source is a gift, but it’s not free to give. Behind every popular repository, there are developers spending nights and weekends fixing bugs, writing documentation, and handling pull requests—often without a single dollar in return. Community goodwill alone doesn’t pay server bills, fund major rewrites, or keep core contributors from burning out. That’s where dual licensing steps in as one of the most effective—and most misunderstood—sustainability models in open source.

The simple idea behind dual licensing

Dual licensing means offering the same piece of software under two different sets of terms. Typically, one license is a permissive open source license (like MIT or GPL), and the other is a proprietary commercial license. Users get to choose which one fits their needs—and their wallet.

The catch? The open source license often includes a “copyleft” clause (most commonly the GNU General Public License, or GPL) that forces derivative works to also be open source. This is great for community projects, but it’s a dealbreaker for companies that want to embed the code in a closed-source commercial product. For them, the commercial license is a clean escape hatch—and the project gets paid.

Why copyleft is the secret sauce

If you dual-license under MIT or Apache 2.0, there’s no real incentive for companies to pay. They can just take the code, use it however they want, and never contribute back. That’s why the most successful dual-license projects use the GPL or AGPL as the open source option.

The AGPL is especially powerful for SaaS companies. Under the standard GPL, if you run modified code on your own servers and never distribute it, you’re not required to release your changes. The AGPL closes that loophole: any network interaction counts as distribution. Suddenly, a company using your library in their cloud product has to either open-source their entire stack or buy a commercial license. That’s leverage—and it’s what makes dual licensing work.

Real-world success stories

This isn’t a theoretical model. Some of the most widely used open source projects have built sustainable businesses around dual licensing:

• MySQL — The original darling. MySQL AB offered the GPL version for free, then sold commercial licenses to companies like Google and Facebook who wanted to embed it in proprietary products. Sun Microsystems bought MySQL for $1 billion largely because of that licensing structure.
• Qt — Used by millions of developers for cross-platform UIs. The Qt Company offers Qt under both LGPL/GPL and a commercial license with support and additional modules. It’s the backbone of their revenue model.
• MongoDB — Uses the Server Side Public License (SSPL), a custom license designed to prevent cloud giants from offering MongoDB-as-a-service without paying. Not exactly GPL, but the same dual-license strategy.
• Redis — Recently moved to a dual-license model (Redis Source Available License + SSPL) to protect against AWS, Google, and Microsoft offering hosted versions without contributing back.

Each of these projects faced the same scenario: their code was being exploited by deep-pocketed companies who gave nothing in return. Dual licensing gave them a way to ask for value.

But it’s not a magic wand

Dual licensing comes with real trade-offs. The most obvious: you’re intentionally creating friction for open source adoption. Some developers will avoid your project because of the GPL. Corporate legal teams might block it entirely. You’re choosing a smaller, more committed community over viral adoption.

There’s also the enforcement burden. If you don’t actively pursue companies that violate your license, the commercial license becomes worthless. That means legal costs, C&D letters, and occasionally, lawsuits. Not every project has the stomach or the budget for that.

And then there’s the “benevolent dictator” problem. Dual licensing works best when a single entity owns the copyright to all the code. If you accept contributions from the community without a contributor license agreement (CLA), you lose control—you can’t relicense their code under the commercial terms. Many dual-license projects require CLA-signing for every pull request, which can deter casual contributors.

When dual licensing makes sense

If you’re building a library, framework, or tool that’s directly embeddable into commercial products, dual licensing is a natural fit. Think databases, UI toolkits, authentication libraries, or WebRTC stacks. Anything that a company would want to ship as part of their own product, rather than just use as a standalone tool.

If your project is more of an end-user application (a CMS, a game engine, a self-hosted analytics dashboard), the dual-license model is harder to pull off. Companies might use it internally, but they’re less likely to distribute it—so the GPL’s leverage fades. In that case, open core or donation-based models might work better.

The bottom line

Dual licensing isn’t a quick fix for sustainability. It requires a strong legal foundation, active enforcement, and a willingness to sometimes turn away potential users. But when it works, it solves the fundamental tension at the heart of open source: how to give away your work freely while still being able to eat. Licensed right, a single commercial deal can fund a project for years—and keep the community version alive and thriving for everyone else.