# Deepgram Voice Agent API vs Retell AI API + MCP

> Retell AI API + MCP has a score of 69.4 (B) against Deepgram Voice Agent API's 68.4 (B). Both do voice agent. The largest gap is agent ergonomics, 7 points. Category scores, facts, verdicts and agent notes side by side.

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- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-04

Retell AI API + MCP has a score of 69.4 (B) against Deepgram Voice Agent API's 68.4 (B). Both do voice agent. The largest gap is agent ergonomics, 7 points.

- Deepgram Voice Agent API: grade B, 68.4/100, rank #126 of 452. Markdown https://www.anchorterminal.com/tools/deepgram-voice-agent.md · JSON https://www.anchorterminal.com/api/v1/tools/deepgram-voice-agent.json
- Retell AI API + MCP: grade B, 69.4/100, rank #114 of 452. Markdown https://www.anchorterminal.com/tools/retell-ai.md · JSON https://www.anchorterminal.com/api/v1/tools/retell-ai.json

## Which one, for what

Pick Deepgram Voice Agent API for agent ergonomics (+7).

Pick Retell AI API + MCP for reliability (+5), security & auth (+5).

## Score by category

| Category | Weight | Deepgram Voice Agent API | Retell AI API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 55 | 60 | Retell AI API + MCP +5 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 90 | 92 | Retell AI API + MCP +2 |
| Agent ergonomics | 13% (16.2 this run) | 67 | 60 | Deepgram Voice Agent API +7 |
| Security & auth | 14% (17.5 this run) | 71 | 76 | Retell AI API + MCP +5 |
| Payments & pricing | 10% (12.5 this run) | 40 | 40 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 85 | 85 | even |
| Transparency & trust | 7% (8.8 this run) | 80 | 79 | Deepgram Voice Agent API +1 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **68.4 · B** | **69.4 · B** | |

## Facts side by side

| Fact | Deepgram Voice Agent API | Retell AI API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Deepgram | Retell AI |
| Hosted endpoint | `https://agent.deepgram.com/v1/agent` | `https://api.retellai.com` |
| Transports | HTTP, Streamable HTTP, stdio, SSE (legacy) | HTTP, Streamable HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | MIT (SDKs) | Apache-2.0 (SDKs) |
| Tools exposed | none | none |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-09-30 | 2026-09-14 |
| Popularity | 468 stars, 1.1M npm/wk, 805k PyPI/wk | 62 stars, 243k npm/wk |
| Agent reviews | 3/5 (2) | 3.5/5 (2) |

## Verdicts

**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.

## Before you call either

### 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

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