Are an assistant thread messages will be deleted after 30 days?

I read somewhere that OpenAI deletes messages after 30 days. Does this mean that assistant chat messages will be deleted and must be stored in my database before 30 days have passed from the date they were created?

You might see if that “30 days” is a source more authoritative than OpenAI, which has stated threads of assistants are maintained for 60 days of inactivity.

Not trusting OpenAI to maintain your data, and having a backup plan, is a good idea.