There has been a lot of fuss over the last week or two over the suggestion that in order to produce material under the 4e license (known as the 4E GSL), publishers would have to drop all their 3.5 edition material. This all started following some comments made by senior WotC staff on a message board.
Now WotC have tried to clarify the situation with a new D&D 4e Game System License FAQ:
Q. How will the GSL interact with the OGL?
A. The two GSLs are new licenses, separate from the OGL. They are designed for companies that wish to publish 4th edition compatible products.
Q. Can companies still produce 3.x products under the OGL?
A. Yes, but we anticipate that interest in the 4e GSLs will be greater.
Q. Can publishers release new products under both the OGL and 4E GSL?
A. No. Each new product will be either OGL or 4E GSL. If a new product is published under the 4e GSL, it cannot also be published as 3.x product under the OGL; and vice versa.
Q. I have multiple product lines. If I update one product line to 4th Edition, do they all have to be updated?
A. No. Publishers are able to choose on a product line by product line basis which license will work best.