As I understand it, it can mean one of two things: - Applications compiled in 10.10 will run in 10.11 - Third-party frameworks compiled in 10.10 can be used t

As I understand it, it can mean one of two things: - Applications compiled in 10.10 will run in 10.11 - Third-party frameworks compiled in 10.10 can be used to compile applications in 10.11 Those are different concerns, and (at least from what I've seen), it seems that Apple has promised the first but not the second.