If you claim them before September 19th, you can now get all five expansion packs for Battlefield 4 for free. This comes a month before Battlefield 1 launches, and it hopes to get people hooked further into the gameplay style, wanting more in a month's time. They have occasionally been through the “On the House” promotion in the past, on an individual basis, but this is the first time that they're all free, together.
It seems to be…
This will probably upset some Battlefield 4 Premium owners, but, even though I'm one of them, I don't think it's that big of a deal. It's fine for EA to give away their own content whenever they like, and, even still, paying customers bought access to it for over three years before it was given away.
I should note that you need to own the game, itself, though. It currently costs $19.99, although it's recently been available for $5, so hopefully you picked it up by then.