From the announcement:
4th Edition is bigger (and smaller) than ever, with a new rulebook that is slimmer than previous editions but retains all the tactical challenges that you have come to expect from Flames Of War. Accompanying the book will be a massive range of new plastic models as we once again return to Mid-war in the desert.
The 4th Edition Mid-war range is now available for pre-order in the online store. Just check on the name of the product you'd like to pre-order from the release schedule below and you'll be taken directly to the online store.