From Facebook Developer Wiki

How can I tell which version of the PHP API I am currently using and which version is currently offered? There doesn't appear to be any version information inside the README or the .php files and there doesn't appear to be any version information offered online here or appended to the downloaded tarball.

We don't do versioning. We update the client when we release a new feature, so when that happens, you can download the client then. It's a really good idea to subscribe the Developer blog and the Platform Live Status, where we make all our announcements. Also, the Live Status feed gives you current information about the state of Facebook Platform in addition to alerts and important notifications. Pete -- 563683308 18:06, 18 November 2009 (PST)