Aaron Plattner mentioned the new long-lived driver series in this NvNews.net thread and made the following comment:
275.28 released as the current long-lived branch release.
This is a new category of releases, so I think it needs a little explanation. We've started maintaining longer-lived release branches that only take critical or low-risk fixes. These releases are intended for users of non-legacy GPUs who don't necessarily need the latest and greatest features. If you've ever used Ubuntu's LTS releases, these should be a similar idea.