Currently, statuses beginning with "@username" are marked in our system as being in reply to the username specified, as well as in reply to that user's current status ID. For example: if I update my status to be "@mzsanford How's that project going?", my status' in_reply_to_status_id attribute will be the ID of Matt's most recent update.
Starting later this week, we will no longer be automatically populating the in_reply_to_status_id attribute of statuses. If your application wants to specify that a status is in reply to a specific status ID, please include the in_reply_to_status_id parameter when POSTing to /statuses/update. We will continue to populate the in_reply_to_user_id attribute based on the screen_name at the the beginning of an @reply-style tweet. This means that even if you don't specify the particular status ID you're replying to, you can still ensure that a status will show up in another user's /statuses/replies feed (and the "Replies" tab on the Twitter website). This is all a bit confusing, but it boils down to this: 1. If you're replying to a particular tweet, make sure to include that tweet's ID in the in_reply_to_status_id parameter in addition to ensuring that "@username" begins the body of the update. 2. If you just want to post a public tweet to another user, start tweets with "@username" like you always have. Hopefully, a very minor change. Let us know if you have any questions. -- Alex Payne - API Lead, Twitter, Inc. http://twitter.com/al3x
