White Scars are rumored to be the first Space Marine codex supplement, although it appears not to be coming immediately, as nothing can be found in the September White Dwarf mentioning it. However, we have had previous rumors here on Faeit 212, saying that the supplement was very much complete, indicating that will be first and soon after the codex release. Perhaps part of an October release?
Please remember that these are rumors.
via a reader from the Faeit 212 inbox
It's not gone unnoticed by the community as a whole that there is a trend in regards to Black Library releases and codexes and I thought it interesting how there was a 12 part series called 'Scars' that began this week on the BL website. The last book in the series looks to be released on October 23rd.
via an anonymous source from Faeit 212 (old post, with more information)
White Scars is one of the supplement codexes, and it is also complete (borderline printed) so logic dictates it'll be released a few weeks after the SM codex, but I don't have a street date for you.