The 0.10.x versions will be tracking syntax from PHP versions 7.1.x and are runnable on PHP 7.1+.
Please use version 0.8.x if you're using a version of PHP < 7.1.
See the file NEWS for what has changed in this version.
Phan 0.10.x versions are similar to the corresponding 0.9.x versions, except that they use AST version 50 instead of 40. As a result, Phan 0.10.x requires php-ast 0.1.5+, while 0.9.x requires php-ast 0.1.4+.
If a project uses third party phan plugins, those plugins may need to be upgraded.
Users of Phan 0.9.x versions should upgrade to 0.10.x when possible.