If you intend to launch a closed-source* product at some future date and pay the per-unit licensing fees, the developer needs a seat license from day one.
(* closed-source or code that statically links in the Qt libraries)
* Not accusing you of course; I'm totally convinced that it can come from a misguided sales rep trying to close a deal as early as possible.
*NOTE: If Licensee, or another third party, has, at any time, developed or distributed all (or any portions of) the Application(s) using an open source version of Qt licensed under the terms of the GNU Lesser General Public License, version 2.1 or later (“LGPL”) or the GNU General Public License version 2.0 or later (“GPL”), Licensee may contact The Qt Company via email to address sales@qt.io to ask for the necessary permission to combine such development work with the Licensed Software. The Qt Company shall evaluate Licensee´s request, and respond to the request with estimated license costs and other applicable terms and details relating to the permission for the Licensee, depending on the actual situation in question. Copies of the licenses referred to above are located at http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html, http://www.gnu.org/licenses/lgpl-3.0.html, http://www.fsf.org/licensing/licenses/info/GPLv2.html, and http://www.gnu.org/copyleft/gpl-3.0.html.
So really the questionable term isn't an additional term on the LGPL, it is on the commercial license.
I think this is mostly meant to avoid having a team of 50 develop an internal version based on LGPL, and then a team of 1 maintain the commercial version, paying a single developer seat.
Note that you can still do a throw away prototype without problems. Some say you should in any case!
You're right, it does sound a bit nasty. No, I haven't read the license myself. It's been brought up multiple times on official Qt blog comments and mailing lists, though.
Edit: checked it now, and it's clearly written at https://www.qt.io/faq/, "Developing with a Commercial License":
> Q: If I have started development of a project using the open source version (LGPL), can I later purchase a commercial version of Qt and move my code under that license?
> A: This is not permitted without written consent from The Qt Company. If you have already started the development with an open-source version of Qt, please contact The Qt Company to resolve the issue.
OSS was a completely different animal back when this thing started. And it was forward thinking to avoid the whole problem with people demanding free support and bugfixes for open-source code.
If your project decides to go commercial the initial license term will include a cost of conversion based on the quantity of code already written.
It would be interesting if they expressed that rate as something like:
A gz -1 compressed tarball of the affected source code will be created, the size (in bytes) multiplied by X is the maximum fee we would charge for retroactive licensing.
I choose the wording 'maximum' there as it still allows them to offer better deals under other circumstances.
It's always been explained to me by the sales people that "you cannot switch licensing models mid-stream". So if you're planning to go commercial, you start commercial.
It's not really about closing the deal as much as making sure the Trolltech developers were paid during the time you needed their support.
The OSS license doesn't grant you any support from Trolltech, does it?
