Yup, you read that right - now through Oct 13th via iTunes. Here are the instructions from one user since it doesn't appear under "Purchased" for some people:

I went to the iTunes store, searched for U2, clicked on the new album, and it showed up with the usual greyed-out, un-clickable 'purchased' button. clicking on the album icon above makes the page re-load and I noticed that the grey 'purchased' button (very) briefly switched to a white 'free' button. Marshalling all of my iOS game-playing reaction-time training, I clicked the album and quickly clicked the 'free' button before it switched to 'purchased'.