20 years ago, Trolltech, the company that created Qt, was founded. One of its founding principles was to release Qt as free software to the open source community. In the early versions, this was limited to Unix/Linux and the X11 windowing system. Over the years, more and more platforms were included into the open source version of Qt.
At the same time, the licenses under which Qt was available evolved. The Qt 1.x source code was still released under a rather restrictive license. With Qt 2, we moved over to the QPL. Some years later, with Qt 4.0, Qt started to embrace the GPL v2, to remove some license conflicts between GPL-based applications and the QPL.
Trolltech was involved in talks with the Free Software Foundation (FSF) when the GPL v3 was created, and we added this license as an optional license for Qt after it was published by the FSF. Finally, in 2009 Nokia added LGPL v2.1 as a licensing option to Qt.
The spirit of all GNU licenses is about a strong copyleft, giving users rather strong access and rights to the source code of application and libraries. It was always meant to protect the users’ freedom to modify the application and underlying libraries and run the modified application.
In many people’s opinion there is, however, a loophole in the LGPL 2.1, where it doesn’t clearly talk about running the applications using a modified version of the library. Even though it violates the spirit and intentions of the LGPL, this loophole has been extensively used by companies that create locked-down devices. If devices use LGPL v2.1 software, the user may not be able to install modified versions of the library on the device and use it together with the other software that is installed on it.
We also consider locked-down consumer devices using the LGPL’ed version of Qt to be harmful for the Qt ecosystem. The device is not open to third party developers and thus doesn’t contribute in extending the size of the Qt ecosystem and the range of devices that can be targeted by software developers using Qt. In addition to not contributing to the ecosystem, it doesn’t fund the further development of Qt.
For these reasons we believe that LGPL v2.1 is not protecting the users’ freedom as it was intended by the Free Software Foundation. To account for this, the FSF created version 3 of the LGPL, a license we feel is legally formalizing the intentions of the earlier version.
Changes in the Qt 5.4 Release with LGPLv3
Because of this, we are now adding LGPL v3 as a licensing option to Qt 5.4 in addition to LGPL v2.1. All modules that are part of Qt 5.3 are currently released under LGPL v2.1, GPL v3 and the commercial license. Starting with Qt 5.4, they will be released under LGPL v2.1, LGPL v3 and the commercial license.
However, there will be a set of new add-ons that will be only released under LGPL v3 (plus GPL v2 or later) or commercial license. These add-ons are listed below. We have discussed with the KDE Free Qt Foundation and have their support to make this change in Qt 5.4. We are also in talks with the KDE Free Qt Foundation about further strengthening the agreement.
New add-ons released under LGPL v3
In Qt 5.4, the new Qt WebEngine module will be released under LGPL v3 in the open source version and under a LGPLv2.1/commercial combination for Qt Enterprise customers.
Adding LGPLv3 will also allow us to release a few other add-ons that Digia before intended to make available solely under the enterprise license. In Qt 5.4, we will add a technology preview for two brand new modules to Qt under the LGPL v3.
The second module is a lightweight WebView module that will also be released as a technology preview. It supports embedding the native Web engines of the underlying operating system into Qt, and is currently supported on Android.
There is a final add-on that will get released under LGPL v3. This module will give native look and feel to the Qt Quick Controls on Android. This module can’t be released under LGPL v2.1, as it has to use code that is licensed under Apache 2.0, a license that is incompatible with LGPL v2.1, but compatible with LGPL v3.
How does this change affect you as a Qt user?
One of the first questions you might have is, of course, how this affects you as a user of Qt.
This first thing to notice is that if you are using Qt under a commercial license, nothing changes at all.
Also, if you are using Qt under GPL v3, you are unaffected, since LGPLv3 can always be converted to GPLv3.
All modules that existed in Qt 5.3 will still be available under LGPL v2.1. So if you are using Qt under the GPL v2 or LGPL v2.1, nothing changes as long as you don’t use any of the new modules that are only available under LGPL v3. If you start using those, your source code will fall under the conditions given by the LGPL v3 (or GPL v2).
These changes will be effective in Qt 5.4 Alpha. I believe that adding LGPL v3 as a licensing option will help both Qt and the open source ecosystem. It is a lot clearer about the intent of the LGPL license and its use in Free Software.
Please find more information about open source licenses at http://www.gnu.org/licenses/.
If you are not sure what license you should be using in your project, please consult a legal expert.
Digia has opened an email address for specific questions about using Lgplv3 in your project. Please contact us via Qtlicensing@digia.com.