Two months after the release of Rock Band 4, you can finally import the soundtrack from Rock Band 3 for use in the latest game in the series.
Over the past few days, Harmonix has added the Rock Band 3 export feature for both PS4 and Xbox One players. This functionality was expected out earlier this month, but is now in place on both platforms in North America. Players in Europe can expect to see it sometime this week.
This process, which costs $15, exports all 83 songs from Rock Band 3. It can't be done from the Xbox Live or PSN stores; it has to be done through Rock Band 4's in-game store.
Assuming you're already verified as an owner of Rock Band 3, you can purchase the export option from the "Get More Songs" screen in Rock Band 4. The process is fairly similar on both Xbox One and PS4, but a step-by-step breakdown is available on Harmonix's website. You can also find a list of exactly which games' can still be imported into Rock Band 4 here.
Keep in mind that you need to be a verified owner of Rock Band 3 within the same console family--you can't move songs from the Xbox 360 version of Rock Band 3 to Rock Band 4 on PS4, for instance.
Last week, Rock Band 4 added a new, incredibly hard difficulty mode, Brutal.