Qt 6 is a major version, and migrating a real Qt 5 application to it is more than a recompile. The framework was modularised, the build system shifted toward CMake, some APIs were removed or replaced, and modules moved around. None of it is insurmountable, but a successful migration is planned, not stumbled into. This guide covers what changed and how to approach the move in 2026.
TL;DR
Qt 6 is a major release with breaking changes: a modularised structure, CMake as the primary build system, removed and replaced APIs, and relocated modules
The build-system move from qmake to CMake is often the biggest single piece of work
Migrate incrementally where possible, using the compatibility helpers Qt provides, and rely on your test suite to catch regressions
