Every LLM interaction produces data you could store: the prompt, the completion, the retrieved context, the user who asked. Keeping all of it makes debugging and evals easy — and creates a growing pile of potentially sensitive records that is a breach liability and a compliance obligation. Retention policy is where you balance those two honestly, per data type.
Decide what to log, at what fidelity
Not everything deserves the same treatment. Separate the operational metadata you genuinely need from the sensitive content you should minimise:
| Data | Keep | Note |
|---|---|---|
| Token counts, latency, model, prompt version | Long | Cheap, non-sensitive, drives cost and quality analysis. |
| Prompts / completions with PII | Short or redacted | Highest liability; redact before storing, short window. |
| Prompts / completions, no PII | Medium | Useful for evals and debugging; still set a window. |
| Retrieved documents | Reference, don't copy | Log the document id, not the full text. |
Set and enforce retention windows
Every category needs an expiry, and the expiry needs to be automatic. A policy that says "delete after 30 days" but relies on someone remembering is not a policy. Use TTLs on the store, or a scheduled job that purges past the window, so old data deletes itself. Keep the cheap metadata longer and the sensitive content as briefly as your debugging genuinely requires.
Provider-side retention
Remember the provider keeps its own copy of your API inputs for a period. Know that window, and for sensitive workloads use the provider's zero-retention or enterprise option so nothing is stored beyond the request. Your retention policy is only as tight as the looser of your side and theirs.
Privacy law gives users the right to have their data erased, and "we can't find it" is not a compliant answer. Tag stored interactions with a user id so a deletion request is a targeted purge, not an impossible search. Design for deletion before you are legally required to perform one.
Retention is a deliberate default, not an accident of infinite disk. Log the cheap metadata generously, minimise and time-box the sensitive content, align with the provider's retention, and make per-user deletion a routine operation. The data you have thoughtfully chosen not to keep is data that can never be breached or subpoenaed.
Independent software engineer in Nairobi specialising in Acumatica customisations, Laravel backends, and tax fiscalisation integrations across East and Southern Africa.