ActionScript 3 Player APIs, both in the chromeless and embedded variety, have been available for use since Oct'09. During the launch, Google the deprecation of ActionScript 2 equivalents. As per deprecation policy, Google'll keep ActionScript 2 Player APIs running through Oct'2012.
However, there's a change; "As of Jan'11, some videos that YouTube and our content partners would like to monetize willn't be playable using ActionScript 2 chromeless player because it doesn't have ability to show ads. If you play such a video, an onError event will be fired, as documented in ActionScript 2 Player reference guide. As a developer, you can handle this event and play an alternate video, or display an explanatory message to your users," explained Google.