Do OpenAI Assistant API thread messages expire or are they retained indefinitely?

Based on the current documentation for the API endpoints, there isn’t any mention of an expiration mechanism for threads or messages. The API simply provides a way to retrieve all messages associated with a given thread. The "limit" parameter is only used to control pagination—i.e., it sets the maximum number of messages returned in one API call (between 1 and 100). This doesn’t imply that older messages (beyond the limit) are removed or expire; rather, you’d need to paginate through the list or adjust your queries to retrieve additional messages if a thread has more than 100 entries.

In summary:

• Message Retention: There’s no documented expiration for threads or messages; they persist until deleted or modified by your application or any future changes in OpenAI’s policies.
• Limit Parameter: The limit simply caps the number of messages returned in a single API call, not the total count of messages stored or available in the thread.

If retention policies ever change or additional details become available, they would be updated in the documentation. For now, you can assume that messages are stored indefinitely (subject to your account and usage terms).