Two windows, set per workspace, because audio and text are different risks: the audio is a person's voice and the text is what they said, and a policy that deletes the audio after thirty days while keeping the transcript for a year is a normal thing to want.
Both default to 90 days. That is deliberate — the alternative default, keeping everything forever, is exactly what the retention question on every security questionnaire is asking about, and a default nobody opens is the only setting most workspaces will ever have. You can set either window to any whole number of days from one to ten years in Settings → Call data, or choose to keep data indefinitely, which has to be selected deliberately and is recorded when it is.
A sweep runs twice a day. For every conversation past its window it computes the SHA-256 of the recording and of the transcript, writes those hashes into your workspace's audit trail as a receipt, and only then deletes the object, the transcript segments and the summary. The receipt is written first and the write cannot be skipped: if the trail cannot be written, the data is not deleted. An unrecorded deletion is indistinguishable from data loss, and we would rather keep data a day longer than be unable to prove we removed it.
The conversation record itself survives the sweep, with its audio and words gone and the proof of what used to be there on the row. It was billed and it is in a month's numbers; deleting it would quietly rewrite your own reporting.
Backups are the exception every honest DPA has to name: a deleted recording can persist in an encrypted database backup until that backup rolls out of its own cycle. Backups are never used to serve a request and are restored only to recover the platform after a failure.