[bradfa]

Qt (the company) releases MOST of their code under open source licenses, but not all. Qt4 was LGPLv2.1, Qt5 and beyond are under LGPLv3.

In every major Qt release, there's a handful of super useful but kind of niche widgets which aren't released under open source licenses, presumably as a sales tactic as buying licenses gets you these widgets and sometimes that is cheaper than building them yourself, but unless you need these, you probably don't care about this.

Although my experience attempting to buy licenses from Qt is about a decade out of date now, the way it roughly worked was you paid a per-seat-per-year fee to get a developer license or build-machine license. Then you bought bundles of deployment licenses, and the bigger the bundle then the lower the cost per license. If you are buying a bundle of a few thousand devices then you pay more per license than if you're buying a bundle of a few million. Either way, it is a significant chunk of cash you have to front to get your block of licenses and normally embedded projects are EXTREMELY sensitive to per-unit costs.