### Answer No, the information you send via the API during an outbound call (such as

retell_llm_dynamic_variables

or

metadata

) is specific to that particular call and does not automatically persist for future inbound calls from the same number. [(1) ]() When you create an outbound call, parameters like

retell_llm_dynamic_variables

and

metadata

are described as: - `metadata`: "An arbitrary object for storage purpose only... Not used for processing." - `retell_llm_dynamic_variables`: Injects into "your Response Engine prompt and tool description" for that call. These are tied to the individual call, not to the phone number or caller relationship. To pass dynamic variables on inbound callbacks, you would need to use the

inbound_webhook_url

on your phone number configuration. [(2) ]() This webhook fires for inbound calls and allows you to "override agent id, set dynamic variables and other fields specific to that call." So if you want returning callers to have their information available, you'd need to: 1. Store the caller's data externally (e.g., in your own database keyed by phone number) 2. Use the inbound webhook to look up and inject that data via

retell_llm_dynamic_variables

when they call back

​ To learn more, see the sources I considered: [[1] Create Phone Call](https://docs.retellai.com/api-references/create-phone-call) [[2] Update Phone Number](https://docs.retellai.com/api-references/update-phone-number) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

### Answer The webhook has a timeout of 10 seconds to return a response. [(1) ]() Whether lookups from thousands of records are "slow" depends entirely on how you implement your external database and lookup logic—not on Retell itself. With proper indexing (e.g., indexing by phone number) , database lookups are typically very fast (milliseconds) , even with large datasets. As long as your webhook responds within the 10-second timeout window, Retell will accept the dynamic variables you return. If your lookup takes longer than 10 seconds, the webhook will fail and retry up to 3 times. For high-volume use cases, consider using a fast key-value store or caching layer to ensure quick lookups by phone number.

​ To learn more, see the sources I considered: [[1] Webhook Overview](https://docs.retellai.com/features/webhook-overview) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.