Last friday at FITC Adobe announced that the next Flash Player's version number will be 9, not 8.5 (the previously announced version number). The version number change reflects the vast amount of new functionality that will be added to the next player, including the new ActionScript 3.0 programming language.
Flash Player 9 will mark the first time a major Flash Player release has been made available before its accompanying Flash authoring tool. The next Flash authoring tool, code named Blaze, is expected to target Flash Player 9. Blaze does not yet have a release date, but a preview release that supports ActionScript 3.0 is expected to be made available through Adobe Labs.
Hence, developers wishing to produce Flash Player 9 content in ActionScript 3.0 will be able to choose from three development options:
Mike Chambers, of Adobe developer relations, has a good overview of how ActionScript 3.0, Flash, Flex, and Flash Player 9 all fit together.