Jan 13

Qt temperatures drop from January to June

I’ve previously talked about how the Qt 5 Winter is coming. Since we started talking about that, people have begun asking what are the date limits for each thing, when the API would freeze, when Qt 5.0 would be stable, when we’d release, etc. This blog tries to answer that a little.

Last month, we were preparing a list of features that needed to be done for Qt 5.0. The result of that activity is Task QTBUG-20885, which is a meta-task containing as sub-tasks everything that needs to happen for Qt 5.0′s feature freeze. Those are the changes that must go into Qt 5.0 and not in any later release. They are major refactorings or other changes that would break source- or binary-compatibility.

That task is now mostly accomplished. Lars has suggested a feature freeze date of February 4th, on his post on the Qt development mailing list. There’s not a lot of time left, so if you have something that needs to go in and hasn’t been taken into account, create the task and post now to the mailing list.

What happens next? Well, I don’t have dates, but I can tell you what will be[1] the stages of API freezing for Qt 5.0:

  • Alpha (Feature freeze): the first step, where all the features are in and work as best we can determine, in all the reference platforms[2] of Qt. The purpose of the Alpha release is to validate the API and get feedback from our own developers as well as bleeding-edge testers whether the code really works and solves the problems it was intended to. Since the point of the Alpha release is to get feedback on the API and whether it works, the API is definitely not frozen at this point. After this point, no new features are accepted.
  • Beta: the API is soft-frozen, which means it will almost not change anymore. Most of the feedback that we expected to receive regarding the API has been received and acted upon. From this point on, early users of Qt can start depending on the API. If any further API changes are required, they can still be done but must be clearly documented and communicated to those early users. The purpose of the Beta release is to start using the API and to start validating the implementation of the solutions present. That means the focus after the Beta release is to discover issues and fix bugs, not to completely refactor something that isn’t solving the problems.
  • Release Candidate: the API is now deep-frozen and will not change unless a catastrophic flaw is discovered. If that happens, the developer who wants to change the API must convince the Release Team to postpone the release. At this time, the ABI (binary compatibility) should be soft-frozen too, but issues with it may still be solved.
  • Final Release: the API and ABI is completely frozen; the source- and binary-compatibilities of Qt kick in. This release will be called Qt 5.0.0. All programs compiled with this release will run without recompilation on any Qt 5.x.y release. Additionally, any programs compiled with Qt 5.0.y will also run without recompilation on Qt 5.0.0.
  • Patch Releases: the Qt 5.0.y releases, to be had in the second half of this year, fixing issues reported, but not adding new features.

There should be only one alpha release, sometime next month. There may be multiple beta releases, as time progresses and issues are fixed. The point of a beta is to find more issues, so we need to release often for our users to give feedback. There’s also likely going to be only one release candidate, but it’s possible to have more than one as we find issues. And ideally, the final release should be just the last RC rebadged, but history shows we will add a few minor fixes between the two.

This process may not be followed exactly as I listed, though. Given the number of important new features, Lars has said that he might accept new features past the freeze date, provided we can see that there is progress. In other words, we will not wait for features we’re not certain will be delivered soon.

Finally, this process applies only to Qt 5.0. The process for Qt 5.1 and onwards should be different. For one thing, those releases will not have BC breakages, so the provisions relating to BC will not apply. For another, we plan to put in place a different branching model (subject for another blog) and keep the Qt Project maintainers true to their duty of “code is always ready for beta,” meaning that the feedback we’re scheduling for the period between alpha and beta right now should happen before the feature is accepted into the mainline.

Happy hacking.


  1. The list presented is the one I sent to the mailing list in December. Lars agreed to it and no one else challenged.
  2. The current reference platforms for Qt are: Windows; Mac OS X 10.6 and above, using Cocoa, Linux using XCB; and Linux using Wayland.


  1. avatar
    Quim Gil

    Great! Can we have this information in a wiki page not far from http://wiki.qt-project.org/5.0_Feature_Requirements please? No hurries & enjoy your weekend. :)

  2. avatar
    Thiago Macieira

    Great idea. I’ll add it there soon.

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