We’re proactively making room for more lists on Twitter by expanding their IDs to 64-bit integers. If you’re using our REST and Streaming APIs, you should confirm that your database, server-side and client-side code consume the safe string-based identifiers represented in “id_str” fields instead of the integer-based identifiers found in the “id” field of Twitter List objects and related references.
To ensure your application’s continued functionality, we strongly recommend modifying your applications to use our string-based IDs whenever present, regardless of the object type.
We’re planning to convert Twitter list IDs within the first few months of 2014 and will make further announcements, as well as updates to the Platform Calendar, as a more firm date is established.
If you have any questions or concerns, please let us know in this thread.