Harmonix detailed how to get your Rock Band 3 songs to Rock Band 4 in a recent blog post:
- The Rock Band 3 export will be available for $14.99 for people that are verified purchasers of Rock Band 3 only.
- Harmonix will be automatically verifying purchases electronically. You’ll need to have bought a new copy and played Rock Band 3 for the export to work.
- Rock Band 3 is expiring, but the export offer will be available for the foreseeable future, as long as you have the game. Harmonix will give plenty of notice before the export offers expires.
- Harmonix is still working on supporting other Rock Band exports in Rock Band 4.
This handy chart may give you more insight into the process:
Rock Band 4 came out October 6 for PlayStation 4 and Xbox One.