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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11For a lower-risk Qt 5 to Qt 6 migration, first bring the application to Qt 5.15, clear deprecated-API warnings, and inventory its modules. Then update the build configuration, port changed APIs and imports, and test graphics behavior on every supported platform. Qt 5.15 is the recommended stepping stone because it is the latest Qt 5 release and minimizes the jump to Qt 6.
What to check before choosing a Qt 6 target
“Qt 6” is not a single, fixed target: module availability and platform support can vary between minor releases. Choose a specific Qt 6 version, then check its module changes, supported configurations, and support terms before editing the project.
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Qt’s release table, checked on October 7, 2026, listed standard support for Qt 6.10.3 through that date and commercial-only standard support for Qt 6.8.6 LTS through October 8, 2029. Those dates are time-sensitive, and support eligibility depends on the release and license. Verify the current Qt release and support table and applicable license terms when selecting a target.
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Also confirm that your compiler, operating systems, architectures, and required Qt modules match the target version. Qt describes its supported configurations as actively maintained and tested; patch releases can drop or replace configurations. Check the Qt 6.10 supported-platforms list for that release, and repeat the check if you select another minor version.
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Step 1: Stabilize the application on Qt 5.15
Before changing major versions, build and test the current application on Qt 5.15. Record the operating systems, architectures, compilers, Qt modules, third-party Qt integrations, and QML imports it actually uses. The Qt porting guide recommends updating to Qt 5.15 before upgrading.
Turn on Qt deprecation diagnostics and resolve warnings while the application still builds against Qt 5.15. To make APIs deprecated through Qt 5.15 a build-time gate, define QT_DISABLE_DEPRECATED_UP_TO=0x050F00. That exposes cleanup work before Qt 6 removes deprecated APIs.
Step 2: Map module, API, and QML changes
Compare each used module and API with the changes for the exact Qt 6 minor version you plan to use. Qt 6 streamlined the framework: modules may be removed, APIs may move, and changes continue across Qt 6 releases. Use the Qt module changes index alongside the Qt 6 porting guide; do not assume a migration note for Qt 6.0 covers a later target.
Do these 3 things before closing this tab:
1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitches- List every linked Qt module and identify its Qt 6 status or replacement.
- Review C++ calls and QML imports for removed, moved, deprecated, or obsolete APIs.
- Check third-party integrations and custom code that depends on Qt-specific build behavior.
Step 3: Choose a build-system path
If the application uses CMake
Decide whether the project targets only one Qt major version or needs a shared source tree for Qt 5.15 and Qt 6. Qt 5.15 introduced versionless targets and commands, which make a dual-version configuration possible. A documented pattern tries Qt 6 first, falls back to Qt 5.15 if Qt 6 is unavailable, and links against Qt::Core:
find_package(Qt6 COMPONENTS Core QUIET)
if (NOT Qt6_FOUND)
find_package(Qt5 5.15 REQUIRED COMPONENTS Core)
endif ()
target_link_libraries(my_app PRIVATE Qt::Core)Use the Qt versioned or versionless target names consistently with the strategy. Versionless aliases resolve to the first Qt major version found in a context; do not mix Qt 5 and Qt 6 in one library or executable. For libraries exported to other projects, versionless targets can create export issues, so versioned targets may be safer. The Qt CMake compatibility guide covers the documented patterns and caveats.
If the application uses qmake
You do not have to move an application to CMake solely to migrate it to Qt 6: qmake remains supported for application builds. Treat custom plugins and libraries separately. Code that depends on Qt 5 build-system internals needs migration to CMake; Qt 6 changed Qt’s own build system to CMake. See Qt’s build-system changes documentation.
Building Qt itself from source is a separate task from building your application. For example, Qt 6.10’s Windows source-build instructions require CMake 3.22 or newer and recommend Ninja. That requirement is not a blanket CMake minimum for application migrations; consult the Qt 6.10 Windows source-build instructions only if you are building Qt from source.
Step 4: Test graphics and high-DPI behavior
Treat QML and graphics as runtime migration work, not just compile fixes. Qt Quick has a new graphics backend, and OpenGL is not guaranteed to be the default on target platforms. If the application calls OpenGL APIs directly, account for the Qt OpenGL module. Verify rendering and effects on the actual backends used by each target platform.
Review high-DPI assets and test at representative display scales, including fractional scaling. Qt 6 changed the default high-DPI rounding policy from Round to PassThrough; some Widgets applications can show visual glitches with fractional scale factors. Where those glitches occur, Qt documents setting the policy to Round to restore the Qt 5 behavior. Validate the result in the application rather than assuming one policy fits every display.
Step 5: Validate the real support matrix
Build and run the port on the application’s actual operating systems, compilers, architectures, and graphics paths. Include QML flows, Widgets layouts, and any integrations identified in the inventory. Test at the display scales your users rely on, and check the chosen Qt minor version’s supported configurations before treating a successful local build as evidence of platform support.
Qt’s documentation cannot establish which regressions a particular application will encounter. Only project-level builds and runtime tests can answer that; record failures by platform and configuration so fixes are not mistaken for universal Qt 6 requirements.
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Can one codebase support Qt 5 and Qt 6?
Yes, a shared source tree can target Qt 5.15 and Qt 6 using conditional CMake package discovery and compatible target names. Qt 5.15 is the useful baseline because it introduced versionless targets and commands. Keep the builds separate: a single library or executable must not combine Qt 5 and Qt 6, and consumers of exported libraries may need versioned targets instead of versionless aliases.
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