This past December we brought the new Direct Message API out of beta to enable you to build more engaging experiences with Direct Messages. This week we are enabling a new approach to Direct Message rate limiting that will help you scale your applications.
Authenticated users may now send up to 5 messages via the API in reply to a message they have received within the last 24 hours. Each message received from a user resets the 24 hour window and the 5 allotted messages that can be sent to that recipient. Each message sent within these parameters will not deduct from the documented daily limit. This is available now to all developers that send Direct Messages via the API using the POST direct_messages/event/new endpoint.
For developers who enable Direct Message creation, we encourage you to migrate to the new POST direct_messages/event/new endpoint to take advantage of this new update and other features. To assist we have a migration guide on developer.twitter.com. As a reminder, not only will migrating enable new features, but the legacy POST direct_messages/new endpoint will be retired on June 19th, 2018 and no longer be functional.