Cinnamon 2.6 reached feature-freeze on the 15th of May and was recently given 2.6 labels. As we’re still bug-fixing it and it’s all very fresh out of the oven it wasn’t officially released/announced yet.

Early builds were added to the “Romeo” section of the LMDE 2 Betsy and Linux Mint 17.1 Rebecca repositories.

If you want to beta-test Cinnamon 2.6:

Launch Software Sources (mintsources) from your application menu

Tick the “Unstable packages (romeo)” checkbox

Click the “Update the cache” button

Use the Update Manager to upgrade the Cinnamon packages (don’t forget the cjs and muffin packages)

Warnings: