PHP 5.6 will only be supported on our servers until December 2020. After that the default version of the PHP settings will automatically be changed to PHP 7.1 (you can change) this at any time.
PHP 7 is a new major version. Basically nothing should stand in the way of a problem-free migration from PHP 5.6 to 7.1, but we recommend that you clarify the following points in advance: