Configure blind transfer modes

Blind transfer sends the active call to a destination without speaking to the destination first. Use it when the destination can accept the call immediately and does not need a spoken introduction.

This guide starts with an existing transfer call tool. To create the tool, configure destinations, and add it to an assistant, follow Transfer call tool.

Both blind modes transfer the caller immediately. The summary variant adds context for a Session Initiation Protocol (SIP) system without speaking that context aloud.

Dashboard mode	API value	Destination experience
Blind Transfer	`blind-transfer`	Receives the call without a message or summary
Blind Transfer with Summary in SIP Header	`blind-transfer-add-summary-to-sip-header`	Receives the call with a generated summary in the `X-Transfer-Summary` SIP header

Blind transfer is the default. If transferPlan is omitted, Vapi uses blind-transfer.

Update the transfer plan on each destination that should use blind transfer.

Dashboard

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Open the transfer destination

In the Vapi Dashboard, open Tools, select the transfer call tool, and expand Destinations. Select the phone-number or SIP destination you want to configure.

Select the transfer mode

Expand Transfer Plan. Under Transfer Mode, select Blind Transfer or Blind Transfer with Summary in SIP Header.

Transfer Mode menu showing the blind and warm transfer options — Select a blind transfer mode in the Dashboard

Choose the SIP behavior for a summary transfer

Complete this step only if you selected Blind Transfer with Summary in SIP Header. Under SIP Verb, select the behavior required by your SIP infrastructure:

REFER — hand the call to the destination (default) sends a SIP REFER.
Dial — bridge a new outbound leg to the destination keeps Vapi in the call path while dialing.
Bye — hang up the Vapi leg only; no transfer is placed and the destination is not dialed is for SIP systems that complete the transfer independently.

If you select Dial, set Dial Timeout (seconds) from 1 to 600 seconds. The default is 60 seconds.

Save the tool

Click Save.

Choose a SIP verb

The SIP verb affects only calls running on SIP telephony. Other telephony providers ignore this setting.

Value	Behavior	Use it when
`refer`	Sends a SIP REFER to hand the call to the destination	The connected PBX or provider supports REFER
`dial`	Dials and bridges a new outbound call leg	The SIP system cannot complete a REFER or Vapi must bridge the destination
`bye`	Ends the Vapi call leg without dialing the configured destination	The SIP system completes the transfer through its own signaling

Do not use bye when you expect Vapi to dial the destination. It intentionally places no destination call.

Verify the transfer

Place a test call and trigger the transfer. Confirm that the destination rings and that the customer and destination can hear each other.

For blind-transfer-add-summary-to-sip-header, inspect the SIP signaling at the receiving private branch exchange (PBX) or provider. Confirm that the destination INVITE or REFER flow contains X-Transfer-Summary and that the value contains the expected summary.

An assistant-forwarded-call ended reason confirms that Vapi initiated the transfer. It does not confirm that the downstream PBX or provider completed it.

Troubleshooting

Symptom	Likely cause	Resolution
The original call ends, but the destination never rings	The SIP system rejected or did not receive the REFER	Check Logs → API Logs, then inspect the provider or PBX SIP logs and packet capture. Confirm required SIP signaling addresses are allowed.
The call ends without dialing a destination	`sipVerb` is set to `bye`	Use `refer` or `dial` when Vapi should place or initiate the transfer.
A dial transfer stops ringing too soon	`dialTimeout` is too short	Increase `dialTimeout` within the 1–600 second range.
The summary header is missing	The standard blind mode is selected or summary generation is disabled	Use `blind-transfer-add-summary-to-sip-header` and enable `summaryPlan`. Inspect the receiving SIP system rather than the audio transcript.
The summary contains the wrong information	The summary prompt is broad or uses the wrong template variable	Give `summaryPlan.messages` a focused instruction and include `{{transcript}}` in the user message.
Vapi shows `assistant-forwarded-call`, but the transfer failed	Vapi initiated the downstream transfer but did not observe its final result	Use the telephony provider’s call detail record and SIP signaling as the source of truth for downstream completion.