Optimize webhook response time (#678)

* Docs: Add assistant-request webhook timeout warning

Co-authored-by: sahil <[email protected]>

* Fix webhook timeout description

Co-authored-by: sahil <[email protected]>

* Fix: Clarify webhook timeout reasons

Co-authored-by: sahil <[email protected]>

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Co-authored-by: Cursor Agent <[email protected]>
Co-authored-by: sahil <[email protected]>

Author: 3 people

fern/server-url/events.mdx

@@ -113,6 +113,14 @@ For inbound phone calls, you can specify the assistant dynamically. If a PhoneNu
 }
 ```
 
+<Note>
+  You must respond to the `assistant-request` webhook within <strong>7.5 seconds end-to-end</strong>. This limit is fixed and not configurable: the telephony provider enforces a 15-second cap, and Vapi reserves ~7.5 seconds for call setup. The timeout value shown elsewhere in the dashboard does not apply to this webhook.
+
+  To avoid timeouts:
+  - Return quickly with an existing <code>assistantId</code> or a minimal assistant, then enrich context asynchronously after the call starts using <a href="/calls/call-features">Live Call Control</a>.
+  - Host your webhook close to <code>us-west-2</code> to reduce latency, and target &lt; ~6s to allow for network jitter.
+</Note>
+
 Respond with either an existing assistant ID, a transient assistant, or transfer destination:
 
 ```json