Deepgram Voice Agent API vs Retell AI API + MCP

Deepgram Voice Agent API

$0.075 a minute all in on Standard, $0.050 with your own LLM and TTS, $200 of credit with no card. No phone numbers or SIP, so you bridge Twilio or another carrier yourself.

Retell AI API + MCP

Published per-minute price for every component, from $0.07 a minute all in. Call data kept indefinitely unless retention is set per agent.

Deepgram Voice Agent API

1. Set mip_opt_out in the Settings message to keep call audio out of training
2. Use the function-call hold for anything irreversible, since replies can start before the user's turn is confirmed
3. Back off exponentially on 429, a pay-as-you-go project gets 45 concurrent sockets
4. Pin the LLM version, an unpinned Gemini route failed for 1.5 hours on 21 July 2026
5. Mint browser tokens with ttl_seconds, not ttl, or they expire after 30 seconds

Retell AI API + MCP

1. Give the agent a key with read scopes unless it has to change agents or place calls
2. Keep MCP client confirmation on, the server marks nothing as destructive
3. Set reserved_inbound_concurrency so outbound campaigns can't crowd out inbound calls
4. Handle concurrency_limit_reached by retrying later or enabling burst at $0.10 a minute extra
5. Set a data retention period on each agent that handles personal data