Scott, The code is here: https://github.com/fl4via/undertow/tree/JAKARTA_EE_9 You just need to fetch that branch and follow the steps: - fetch Batavia project that is used to transform bytes and build it: https://github.com/wildfly-extras/batavia - build Undertow with maven clean install -DskipTests (or do not skip them, but keep in mind they take quite a long time to run) - then use the generated artifacts as dependencies wherever needed: undertow-servlet-jakartaee9 undertow-websockets-jsr-jakartaee9 Since these artifacts are untested, probably you will come back to me with feedback if you find any trouble using them. :-) Feel free to ping me at any time. As soon as this passes, I'll deploy those artifacts to Nexus. Regards, Flavia