PHP7.3.0 が 2018-12-06 にリリースされました。 php.net:archive/2018.php
branch_r1_5 HEAD を PHP7.3 で動作させていますが、 2018-12-28 現在、特に問題は見つかっていません。
The ext_skel utility has been completely redesigned with new options and some old options removed. This is now written in PHP and has no external dependencies.
Support for BeOS has been dropped.
Exceptions thrown due to automatic conversion of warnings into exceptions in EH_THROW mode (e.g. some DateTime exceptions) no longer populate error_get_last() state. As such, they now work the same way as manually thrown exceptions.
TypeError now reports wrong types as int and bool instead of integer and boolean, respectively.
Undefined variables passed to compact() will now be reported as a notice.
getimagesize() and related functions now report the mime type of BMP images as image/bmp instead of image/x-ms-bmp, since the former has been registered with the IANA (see » RFC 7903).
stream_socket_get_name() will now return IPv6 addresses wrapped in brackets. For example "[::1]:1337" will be returned instead of "::1:1337".