We have developed a Python program with a Qt GUI, using the PySide2 bindings. We have so far used the LGPL option of Qt. We were happy with this, as we believe we understand our rights and obligations under the LGPL pretty well.

We currently must consider changing to what Qt calls the "commercial" licensing (nice misnomer, but ok). I cannot describe the reason in detail, sorry, but be assured it is quite silly and not interesting. We are not using any of the commercial libraries such as QtCharts, and we will not do so in the future.

We would very much like to retain the option to

  1. Revert back to LGPL licensing in the future.
  2. Pass parts of our source code to colleagues, who do not have a Qt "commercial" license and do not wish to have one.
  3. Borrow code from these colleagues to incorporate in our program.
  4. Split off sub-libraries from our source code, possibly releasing them as non-free open-source or free open-source software.

The Qt FAQ at https://www.qt.io/faq/tag/qt-commercial-licensing notes

We have started to develop a product with an open source license - How can we upgrade to a commercial Qt license?

You can convert from developing under open source to commercial terms and conditions by contacting the Qt Company. The commercial license does not by default allow using of code created under open source license, thus you will need to contact the Qt Company to help you with the transition.

I am rather worried about the phrasing. Do anyone know what Qt typically imposes as part of this transition? In other words, what freedom do we give up by buying a commercial library?

Note there is a similar question at Changing QT library licence for application from LGPL to commercial that asked whether Qt can do this, not what conditions they typically impose.

Thanks in advance for your comments.

  • I can't tell whether this is a vast overreach or a sensible observation by the Qt FAQ authors: it could easily be either. Do you have a link to, or a copy of, the text of their standard commercial licence? It would be much easier to comment if we could see the actual licence.
    – MadHatter
    Commented Jun 12, 2022 at 6:35
  • Hi @MatHatter, the full license is at qt.io/terms-conditions ; the relevant parts are 3.4 ix, although the conditions for conversion are (I believe) never noted.
    – pietro
    Commented Jun 13, 2022 at 8:23
  • 1
    OK, as I read it, it's fairly sensible. What I think they should have written in the FAQ above is "The commercial license does not by default allow using of code under our open source license", as 3.4(ix) reads to me that if you're a Qt commercial licensee, you cannot also use Qt for other purposes under the Qt open-source licence, which I guess helps avoid unpleasantness.
    – MadHatter
    Commented Jun 13, 2022 at 8:48

1 Answer 1


Long story short, if you used Qt under LGPL (or GPL, no matter which), you can switch to commercial-license anytime, but only if you are owner of entire code written (like being employer of developers).

Or, if you have clear and unambiguous evidence that all non-employees who contributed approve the re-use of their code under the new license (beside old license, I mean, usage of old license can not be avoided, unless explicitly approved).

Note that above assumes that the employment contract forces employees to approve whatever their employer's choice of license is.

In case you can't take a specific individual's approval, well, that's an entirely different question.

  • Thanks for that part, that makes sense, although it seems we also need to get approval from the Qt company. What about the other way around?
    – pietro
    Commented Jun 13, 2022 at 8:26
  • @pietro Above is required no matter the direction (from LGPL or back to LGPL).
    – Top-Master
    Commented Jun 13, 2022 at 9:51
  • I understand, but I'd like to know if Qt allows it.
    – pietro
    Commented Jun 14, 2022 at 10:47
  • @pietro Once above is solved, if you haven't already, all that remains is taking Qt-company's permission to use their commercial-license (which's maybe part of their purchasing process).
    – Top-Master
    Commented Jun 14, 2022 at 14:50
  • I mean, Qt-company has already full-ownership and/or has approvals (of their contributors for their source), hence they can allow you to switch whenever they see fit (which is normally after purchasing).
    – Top-Master
    Commented Jun 14, 2022 at 14:58

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