Qt 6.12 LTS Ships With Built-In QML Hot Reload and a Production-Ready CanvasPainter API
Qt 6.12, released September 30 as a five-year Long-Term Support version, adds native QML hot reload, a production-ready CanvasPainter API and HarmonyOS as an LTS platform.
Editor's Note ·
- Clarification:
- The article describes Qt StyleKit, under 'Styling, models and networking', without noting its status. The Qt blog places it under the heading 'StyleKit Is Available in Labs: Try It Out', meaning it is offered through Qt Labs for trial rather than as a supported Qt 6.12 module.
- Clarification:
- The article quotes Qt as saying Qt 6.12 'is built to meet the requirements set by the CRA'. The Qt blog makes the compliance statement about the commercial Qt 6.12 LTS, and adds that the CRA Declaration of Conformity does not make a product automatically CRA-compliant; developers still have to do their own CRA work.
Overview
The Qt Company published Qt 6.12 on September 30, 2026. According to the Qt blog, the release is a Long-Term Support (LTS) version, which the post describes as one that “gets maintenance over a 5-year period.” The headline changes for developers are native hot reload in the QML engine and a CanvasPainter drawing API that has moved out of preview.
What We Know
QML hot reload
The Qt blog says the QML Engine “has been extended to enable native support of the hot reload mechanism, and the qmlpreview tool has been reworked to use it.” Linuxiac reports that the feature is “available through Qt Creator and the command line using the qmlpreview tool,” and describes the effect as developers being able to see changes to a running QML interface as they edit code, without restarting the application.
CanvasPainter and Canvas2D
Linuxiac reports that CanvasPainter was a Technology Preview in Qt 6.11 and that its core API is now production-ready for both C++ and QML. The Qt blog describes it as an imperative painter-like rendering API for C++ and QML that uses the GPU for hardware acceleration and can use shaders for visual effects. Alongside it, the Qt blog says the Canvas2D API “is modelled after the HTML Canvas, and makes it easy to use JavaScript to draw shapes”; Linuxiac notes that Canvas2D remains in Technology Preview.
Styling, models and networking
The Qt blog says Qt StyleKit “provides a QML-based styling API that lets you style both Widgets and Qt Quick from a single source.” The same post says QRangeModel gains built-in sorting support that lets the model sort its data directly, and that QtGrpc now supports client-side compression of messages, with the available compression algorithms selectable by the developer.
Graphs, controls and WebAssembly
According to Linuxiac, Qt Graphs adds logarithmic axes for 2D graphs, more axis-label customization, and built-in zoom and pan interactions. The same report lists a new QtQuick.Controls.Native style and additional Qt Quick 3D Physics joint types, along with improved audio and video support for WebAssembly and smaller compiled resources through resource deduplication.
Platform and compliance
The Qt blog states: “Starting with Qt 6.12, Qt officially supports HarmonyOS as a Long-Term Support (LTS) platform.” On regulation, the post says Qt 6.12 “is built to meet the requirements set by the CRA as we today know will take effect in December 2027.”
What We Don’t Know
- The sources reviewed do not give a date for when Canvas2D will leave Technology Preview.
- Neither source provides performance figures comparing CanvasPainter with the existing Qt Quick Canvas element.
- The coverage reviewed does not say how the hot reload mechanism handles changes that touch C++ code rather than QML.
Analysis
For teams that standardize on Qt, an LTS release is the version most likely to be adopted for long-lived products, since maintenance runs for five years. Hot reload built into the QML engine, rather than only into an external preview tool, changes the iteration loop for interface work, though the sources do not quantify the gain. How much the CRA statement and the HarmonyOS support matter will depend on the markets a given product targets.