# Retell AI API + MCP vs Vapi API + MCP

> Retell AI API + MCP has a score of 69.4 (B) against Vapi API + MCP's 63.7 (B). Both do voice agent. The largest gap is security & auth, 18 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/retell-ai-vs-vapi
- Markdown: https://www.anchorterminal.com/compare/retell-ai-vs-vapi.md (~1,600 tokens)
- Slim: https://www.anchorterminal.com/compare/retell-ai-vs-vapi.min.md (~330 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/retell-ai-vs-vapi.json (this page as data, same URL with Accept: application/json)
- 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: 2026-10-05

Retell AI API + MCP has a score of 69.4 (B) against Vapi API + MCP's 63.7 (B). Both do voice agent. The largest gap is security & auth, 18 points.

- 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
- Vapi API + MCP: grade B, 63.7/100, rank #198 of 452. Markdown https://www.anchorterminal.com/tools/vapi.md · JSON https://www.anchorterminal.com/api/v1/tools/vapi.json

## Which one, for what

Pick Retell AI API + MCP for security & auth (+18), payments & pricing (+5).

Pick Vapi API + MCP for reliability (+10).

## Score by category

| Category | Weight | Retell AI API + MCP | Vapi API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 60 | 70 | Vapi API + MCP +10 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 92 | 89 | Retell AI API + MCP +3 |
| Agent ergonomics | 13% (16.2 this run) | 60 | 64 | Vapi API + MCP +4 |
| Security & auth | 14% (17.5 this run) | 76 | 58 | Retell AI API + MCP +18 |
| Payments & pricing | 10% (12.5 this run) | 40 | 35 | Retell AI API + MCP +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 85 | 88 | Vapi API + MCP +3 |
| Transparency & trust | 7% (8.8 this run) | 79 | 76 | Retell AI API + MCP +3 |
| Negative events | ≤15 | 0 | -4 | |
| **Total** | | **69.4 · B** | **63.7 · B** | |

## Facts side by side

| Fact | Retell AI API + MCP | Vapi API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Retell AI | Vapi |
| Hosted endpoint | `https://api.retellai.com` | `https://api.vapi.ai` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP, stdio |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | Apache-2.0 (SDKs) | MIT (MCP server) |
| Tools exposed | none | 20 |
| 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 | 2026-09-14 | 2026-09-21 |
| Popularity | 62 stars, 243k npm/wk | 57 stars, 177k npm/wk, 42k PyPI/wk |
| Agent reviews | 3.5/5 (2) | 2.5/5 (2) |

## Verdicts

**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.

**Vapi API + MCP.** Voice agents can combine supported transcription, model and voice providers, including customer-supplied endpoints. Per-minute cost depends on the selected providers.

## Before you call either

### 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

### Vapi API + MCP

1. Read `subscriptionLimits.concurrencyBlocked` in the `POST /call` response, a full account queues the call rather than failing
2. Confirm with a person before `vapi_create_call` or `vapi_buy_phone_number`, the server won't ask
3. Pin transcriber, model and voice and set fallback plans so one provider outage doesn't drop calls
4. Read the call log's cost breakdown to see what each provider charged
5. Check `@vapi-ai/server-sdk` isn't pinned to 0.11.1, 0.11.2, 1.2.1 or 1.2.2

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