From spec point of view, JSF 2.1 is a maintenance release 2 from JSF 2.0, so any application written for JSF 2.0 will work with 2.1 jars. In resume, with JSF 2.1 the following features were added:
<faces-config xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_2_1.xsd" version="2.1"> <faces-config-extension> <facelets-processing> <file-extension>.jspx</file-extension> <process-as>jspx</process-as> </facelets-processing> </faces-config-extension> </faces-config>
There are no major changes between those versions than can cause you incompatibilities. By that reason, in practice both lines (2.0 and 2.1) are maintained by MyFaces Community at the same time.