afraid-scarlet•2w ago
Flush syntax
I want to check if the LLM is actually generating responses with flush syntax, so I’m trying to extract the raw LLM response. I tested with voice.chunkPlan and voice.chunkPlan.formatPlan.enabled = false, but I didn’t see any <flush> tags in the assistant’s output.
https://docs.vapi.ai/assistants/voice-formatting-plan#customizing-the-formatting-plan
I’ve enabled the required configurations for flush syntax, but the results are inconsistent across calls.
https://docs.vapi.ai/assistants/flush-syntax
LLM: OpenAI GPT5 Mini
Voice: ElevenLabs
Has anyone figured out a reliable way to confirm if the LLM is outputting flush tags in its raw response?
Flush syntax | Vapi
Force immediate voice transmission with VAPI's flush syntax for real-time interactions
Voice formatting plan | Vapi
Format LLM output for natural-sounding speech
5 Replies
Hi orthogenius,
To get the LLM to use flush syntax, follow these steps:
1. Flush Configuration: Make sure to use
<flush />, <flush>, or </flush> in the LLM outputs where you want immediate audio feedback.
2. Voice Configuration: Check that voice.chunkPlan has "enabled": true and "formatPlan": { "enabled": true }.
3. Extract Raw LLM Output: Disable other formatting to see flush tags in the raw output by setting voice.chunkPlan.formatPlan.enabled = false.
4. Troubleshooting: If flush tags aren't recognized, check for syntax errors or config issues. You can find more details here.
Test with different scenarios to see how flush syntax works. If issues continue, review your configurations or simulate responses to pinpoint the problem.afraid-scarletOP•2w ago
Thanks for the reply, Pravin
After multiple trials, the LLM did output <flush> tags — I verified this by setting voice.chunkPlan.formatPlan.enabled = false.
Later, I switched to voice.chunkPlan.enabled = true and formatPlan.enabled = true to see how the flush syntax works. But in the call logs during testing, I noticed "flush": false at the points where I had predefined <flush> tags in the system prompt setup.
Could you please provide a call id where that occurred?
afraid-scarletOP•4d ago
Sure
Call IDs where flush configs were enabled but returned "flush": false in call logs:
a19d9b74-36a3-466a-b335-a02faa463817
9f9b5691-4415-4ba1-805f-77d54ad7efcd
Thank you for the call ids. We will look into this and get back to you