From the announcement:
With every new edition of the Flames Of War rules, we have given away free copies to all existing players to say thanks for being a player and welcome to the new version. When we went from version 2 to version 3 we gave away 26 tonnes of books – that's the same weight as a T-34 tank! You might even say that we are Fearless Veterans when it comes to this process.
This time around it is no different, except that you will be getting TWO books, not one.
The first one is a full-sized set of rules, an 112-page, A4-sized book, formatted for existing Early-war and Late-war players. The game rules are identical to the hardback version, only instead of referring to the Unit Cards that we will be using in Mid-war, they refer to the current book range, allowing all existing books to still be used for those two periods.
As well as the rules you will also get a 64-page A5 book containing all the special rules and characters from every 3rd edition book from Early-war and Late-war, detailing how they now work in 4th edition. This is the ultimate Know Your Enemy guide, as every single book in print is covered.