GCC front-ends for 3.4 vs 4.0

[Simon Heath]

Hello, all.  I'm currently in the process of writing a compiler
front-end for GCC, doing all my work using the 3.4.3 sources. 
However, I took a look at the website and it says that the release
date for version 4.0 is April 2005... very soon, in other words.  So
my question is this: Should I stop working with the 3.4 branch and try
to write my front-end for 4.0 instead?  Will the front-end interface
change a lot between 3.4 and 4.0?

Thank you,
Simon