Before you start

Before starting the upgrade check your system for compatibility with a newer TYPO3 version.

  • Enable the deprecation log and let it run for a while while the website is used to catch all deprecations
  • Check installed extensions for versions compatible to the target TYPO3 version
  • Try the upgrade on a development system first!

Handling deprecations

TYPO3 aims at providing a reliable backwards compatibility between versions:

  • Minor versions are always backwards compatible
  • Major versions may contain breaking changes - normally these are deprecated in the version before
  • Most breaking changes usually happen in the first Sprint Release

If PHP classes, methods, constants, functions or parameters are to be removed, they will be marked as deprecated first and not removed until the next major release of TYPO3. For example: a method that gets deprecated in version 9.4.0 will remain fully functional in all 9.x.x releases, but will be removed in version 10.

This strategy gives developers sufficient time to adjust their TYPO3 extensions, assuming many agencies upgrade from one LTS release to the next (usually 1.5 years).

If you notice some API you are using is deprecated, you should look up the corresponding changelog entry and see how to migrate your code corresponding to the documentation.

Read where to find deprecation documentation in the chapter about Check the ChangeLog.