docs: add HIPAA/Zero Data Retention note to variables page (#876)

Author: vapi-tasker[bot]

fern/assistants/dynamic-variables.mdx

@@ -151,4 +151,18 @@ You are a helpful assistant, talking with a customer via {{transport.conversatio
 - Only ask one question at a time
 - Never use Markdown format; write everything as if it is being said aloud
 {%- endif -%}
-```
+```
+
+## HIPAA and Zero Data Retention mode
+
+When HIPAA mode or Zero Data Retention is enabled for your organization or assistant, Vapi does not store any call data, including variable values. This means:
+
+- Variable values passed via `variableValues` are processed during the call but **not persisted** after the call ends
+- Call logs, recordings, and transcriptions are not stored
+- Variables are only available in real-time during the active call session
+
+This ensures compliance with privacy requirements while still allowing you to personalize conversations with dynamic variables.
+
+<Note>
+For more information on enabling HIPAA compliance and understanding data retention policies, see the [HIPAA Compliance](/security-and-privacy/hipaa) documentation.
+</Note>