A Tuesday deadline has been set in which several leading open-source PHP projects plan to stop supporting older versions of PHP in upcoming releases.

The Go PHP 5 campaign, sponsored by several PHP proponents, is intended to move the PHP developer community fully onto the PHP version 5 platform. Among the projects backing the effort are Symfony, Typo3, phpMyAdmin, Drupal, Propel, and Doctrine. These vendors are committing to use PHP 5.2 in releases developed after Tuesday.

Campaign advocates also have issued an invitation to other PHP projects to participate, and so far, about 150 software projects and about 200 Web hosters have committed.

Most PHP Web applications run in PHP 4 and 5. PHP 4 was released in 2000, while PHP 5 became available in 2004.

"We think PHP is absolutely the platform going forward," said Mark de Visser, chief marketing officer at PHP tools vendor Zend Technologies, which is supporting the Go PHP5 effort.

PHP 5 features object orientation, for enterprise application development, and Web services capabilities, de Visser said. But adoption has been slow because of issues like Web hosts that offer PHP 4 by default, Go PHP 5 said.

"No one's moving to PHP 5 because no one wants to be first," said Larry Garfield, a co-founder of the Go PHP 5 project.

Hosts will not upgrade until projects do, but projects will not upgrade until hosts do, thus presenting a chicken-and-egg situation, according to Go PHP 5's July 2007 statement. Go PHP 5 hopes to give Web hosts incentive to upgrade servers to newer versions of PHP.

Additionally, extensions to the PHP 4 platform are ceasing, according to Garfield. There will only be major security issues considered between now and August, and after that, PHP development stops, he said.

PHP 6, meanwhile, is not due for more than a year, de Visser said. It will focus on internationalization, he said.