Ably has introduced Subscription Filters, a new feature that allows subscribers to create custom realtime data feeds by selectively subscribing to receive only part of the data from a channel. This feature benefits publishers by enabling them to create personalized data streams for large numbers of individual clients without worrying about scalability, maintenance, and reliability issues. Subscription Filters can be used in various applications such as chat rooms, social experiences, and data broadcasting. The code demonstrates how to add attributes to messages that can be used for filtering and subscribing to a channel with a filter expression. A demo showcases the feature's functionality in a stock inventory dashboard scenario.