# Why Serial Studio Has a Pro License > Serial Studio is open source and has a paid Pro tier. The honest reasoning: the Qt license history, how the dual license works, and why it stays sustainable. > > Open Source · July 3, 2026 · by Alex Spataru · https://serial-studio.com/blog/why-serial-studio-has-a-pro-license I get a version of this question often: if Serial Studio is open source, why isn't it just free? It is a fair thing to ask, and it deserves an honest answer rather than a marketing one. So here is the whole story, including how the license actually works and why it is built this way. ## How it got here: a Qt licensing decision Serial Studio started out under the MIT license. As it grew, I wanted to use more of Qt, in particular QtGraphs for the plotting. Qt puts those modules under the GPL unless you hold a commercial Qt license, and the MIT license is not compatible with the terms Qt requires there. That left me with a real choice to make. I could relicense the whole app under GPLv3. That keeps it open, but GPLv3 makes commercial use genuinely hard, and plenty of the people relying on Serial Studio at work were not happy about that. Or I could do what Qt itself does: offer it under two licenses at once. GPLv3 for the open-source world, and a commercial license for everyone who needs different terms. I went with the dual license. In effect, I copied Qt's own model and applied it to Serial Studio. ## What the model actually is The important part, and the part people miss, is that the full source is public, including the activation code. I keep it that way on purpose, because I want the software to be auditable. Nothing about how the license works is hidden. Here is what that means in practice: - **Building it yourself produces a GPLv3 build** with the Pro features and the licensing system excluded. It has the same functionality older versions of Serial Studio had, plus the newer improvements: the redesigned dashboard, a friendlier Project Editor, and the performance and stability work. - **The official binaries I distribute are trial builds** that become Pro with a license key. They exist because building, signing, and notarizing binaries (macOS especially) costs real time and money. - **You cannot accidentally compile a Pro build.** Pro requires a valid key and activation ID, and every source file carries an SPDX header that marks it as GPLv3, commercial, or both. The line between the two is explicit, at the file level. - **It all lives in one repository.** I could split Pro and GPLv3 into separate repos, but as a solo developer that would be a lot of extra work, and it would almost certainly leave the GPLv3 build behind and unmaintained. One repo keeps the free build first-class. If you want the free, fully open edition, you build it. That is the standard bargain of open-source software, and there is a [step-by-step guide](https://serial-studio.com/blog/build-serial-studio-from-source) for it. ## Open source is not the same as free support The other half of the answer is about what open source actually promises. Open source gives you the source and the freedom to use, study, modify, and share it. It does not give you a claim on my time, my inbox, upgrades, bug fixes, or maintenance. As one talk on open-source sustainability puts it, people who share their code do not owe you anything beyond the code itself. If you need support, you pay for it. That is not a hostile position, it is just an honest one. The Pro tier is where the prebuilt binaries, the extra features, and the support live, and it is what funds the continued development that keeps the GPLv3 build alive. Both paths are legitimate, and they are aimed at different people. ## Why it has to be sustainable I am one person. Over the years Serial Studio has been used in commercial products with nothing given back, sometimes alongside a rush of conflicting feature requests within a few days, and I have been blamed for problems that five minutes with the README would have solved. I do not say that to complain, but to be clear about what an unfunded solo project actually costs to run. A paid tier is what turns that into a healthier cycle: the people who get real value from the software help it keep existing, whether through funding, ideas, code, or community. Pro on its own may not fully fund the project. But the combination of a trial, a free GPLv3 build you can compile, and a paid tier is what attracts the contributors and supporters that keep it sustainable. There is a wider pattern here that is easy to miss. Most open-source projects do not fail loudly, they simply stop. The maintainer takes a new job, has a kid, loses interest, or burns out, and the commits trail off until the project is quietly abandonware that still ships inside a thousand other people's stacks. A huge share of the software the world runs on is kept alive by one or two unpaid volunteers in their spare time, and that arrangement is far more fragile than it looks. The clearest recent reminder was the [xz-utils backdoor](https://en.wikipedia.org/wiki/XZ_Utils_backdoor) in early 2024. xz is a small compression library that sits deep inside almost every Linux system. It was maintained by a single volunteer who had done years of thankless work, and a hostile actor spent a long time socially engineering their way into co-maintainer status, partly by exploiting that exhaustion and a steady stream of pressure to hand the project off, before planting a backdoor that could have opened a remote door into a huge number of servers. It was caught almost by accident, just before it spread. I am not comparing Serial Studio to xz, or myself to its maintainer, who was the victim of a coordinated attack. But the episode makes a systemic point hard to ignore: when important software rests on one overworked, unfunded, unsupported person, everyone downstream is exposed, and "do it for free, forever" is not a plan. Money is not the enemy of open source. The lack of it is what kills projects and wears down the people who keep them running. I would rather build something that can still be here, and still be well maintained, in ten years. ## A note on the trial, because fairness matters I originally locked features hard when the trial ended, and I came to think that was too harsh. So the trial now resets with each new version. If you are on an expired trial and a new release comes out, you get a fresh 14 days to try what is new. If you want to use it with no interruptions at all, you have two honest options: compile the GPLv3 build yourself, or buy a Pro license. ## Pro and GPLv3, today and later Pro has grown a lot, and it is no longer close to the GPLv3 build the way it was a year ago. Today it adds the advanced drivers (MQTT, Modbus, CAN Bus, audio, USB, HID, and Process I/O), the 3D, XY, waterfall, camera, and Painter widgets, the output and command widgets, MDF4 and the session database with PDF reports, file transfer, operator deployments, and the AI assistant, among others. The GPLv3 build keeps the capable core that most people already rely on. Over time, Pro will keep leaning toward features for businesses and professional use, while the free build stays a solid foundation. There is also a quieter point in all this. The "price" of the free build is stepping out of your comfort zone for half an hour to install Qt and compile it. I have no interest in crippling the GPLv3 build to push upgrades. But someone who takes that half hour has shown they care about the project, and in my experience those are exactly the people who go on to contribute. If that is you, you have earned a voice in where Serial Studio goes, with or without paying a cent. If you value open source, this model was built for you. One path pays with money and the other with time and contribution, and both keep the software healthy. The [pricing page](https://serial-studio.com/pricing) has the details, and [Pro vs Free](https://serial-studio.com/help/pro-vs-free) lays out exactly what sits on each side of the line.