Revolutionize your call operation with Retell
Zero data retention (ZDR) means a provider keeps no copy of your content after processing. What it covers for LLM and voice AI vendors, and what to ask.
Zero data retention (ZDR) is an arrangement in which a service provider processes your content, such as a prompt, a transcript or audio, and keeps no copy of it once the response is returned. The term comes from large language model (LLM) APIs, where it usually means request and response content is excluded from the provider's logs. It is a contract or account setting, not a law or a certification.
ZDR means the model provider does not store your inputs and outputs after the request, but every provider defines the scope differently. Two examples from the providers' own documentation:
So "we have ZDR" is never the full answer. The useful question is: ZDR with whom, for which endpoints, and with what exceptions?
A phone call creates data at several layers, and a ZDR agreement with the LLM covers only one of them.
| Data from one call | Where it is created or held | Covered by an LLM ZDR agreement? |
|---|---|---|
| Live audio | Carrier, speech-to-text provider, voice platform | No |
| Transcript | Speech-to-text provider, voice platform | No |
| Prompt plus transcript sent for each reply | LLM provider | Yes, if the endpoint is in scope |
| Synthesized speech | Text-to-speech provider | No |
| Call recording, logs, tool call data | Voice platform | No |
| Post-call summaries | Voice platform, plus another model call | Depends on that call |
| Timestamps, duration, phone numbers, cost | Voice platform, carrier | Usually kept |
The carrier layer sits partly outside the platform's control. Retell's privacy policy notes that telecommunications providers may process call data as independent controllers for their own purposes, such as billing and fraud prevention.
ZDR also differs from two controls it is often confused with. A retention period stores content and deletes it after a set number of days. PII redaction stores content with identifiers removed. ZDR stores no content at all.
Retell's documentation describes per-agent storage and retention settings rather than a mode called zero data retention. The closest controls:
Storing less has costs. With Basic Attributes Only, the Get Call API no longer returns transcripts or recordings, and PCAP files for debugging SIP failures exist only when storage is set to Everything. For a healthcare setup, see our guide to HIPAA compliance for AI phone agents.
Ask for answers per layer, in writing:
ZDR answers how long data is kept. Data residency answers where it is kept, and a SOC 2 Type II report shows whether the controls held up over an audit period. Ask about all three together; our enterprise voice AI compliance guide covers the DPA review.
If your security review needs per-agent control over what a voice agent stores and for how long, see how the Retell enterprise platform handles it, and test your storage settings on real calls during a pilot.