can I depend on stable PEAR classes to not change?

I've been a PHP programmer for a long time but now that I'm starting some new projects, I'm taking a deeper look at what PEAR has to offer. I'm really impressed. If I write some apps based on PEAR features, but my system is constantly updating my /usr/local/share/pear directory, is it safe to assume that my code can depend on these PEAR classes for a long time? In other words: if I write a webapp that depends on HTML_QuickForm and Auth, for example - will my code be able to work as-is for years, while HTML_QuickForm and Auth are updated? Any insight appreciated. I couldn't find this in the PEAR FAQ. Thanks!