# GPT-Live vs Retell AI API + MCP

> Retell AI scores 69.1 (B) to GPT-Live's 66.8 (B) for voice speech to speech. Prices, MCP, x402, uptime and agent notes side by side.

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- Updated: 2026-10-17

Retell AI API + MCP scores 69.1 (B) on agent readiness against GPT-Live's 66.8 (B), and leads in 4 of 7 scored categories. GPT-Live leads on agent ergonomics. Both do voice speech to speech.

- GPT-Live: grade B, 66.8/100, rank #296 of 1133. Markdown https://www.anchorterminal.com/tools/gpt-live.md · JSON https://www.anchorterminal.com/api/v1/tools/gpt-live.json
- Retell AI API + MCP: grade B, 69.1/100, rank #212 of 1133. Markdown https://www.anchorterminal.com/tools/retell-ai.md · JSON https://www.anchorterminal.com/api/v1/tools/retell-ai.json
- Best conversational voice-agent APIs: https://www.anchorterminal.com/best/voice-agents/index.md
- All 184 voice agents comparisons: https://www.anchorterminal.com/compare/voice-agents/index.md

## Which one, for what

### GPT-Live (B)

Good for: Teams who want a voice front end that keeps talking while a separate backend reasons and runs tools, with WebRTC, WebSocket and SIP from one vendor and a flat per-minute voice price.

Ahead on:
- Agent ergonomics, 76 against 60

Watch for: openai.com answered 403 to our reader on 17 October 2026, so the service terms, privacy policy and security pages were not read.

### Retell AI API + MCP (B)

Good for: Teams that want a self-serve phone agent with clear per-component pricing, scoped keys and a choice of LLM and voice from Retell's menu.

Ahead on:
- Schema & documentation, 92 against 87
- Security & auth, 76 against 66
- Payments & pricing, 40 against 20

Also in its favour:
- Free to start without a card

Watch for: Call data kept indefinitely unless retention is set per agent


## Score by category

| Category | Weight | GPT-Live | Retell AI API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 62 | 60 | GPT-Live +2 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 87 | 92 | Retell AI API + MCP +5 |
| Agent ergonomics | 13% (16.2 this run) | 76 | 60 | GPT-Live +16 |
| Security & auth | 14% (17.5 this run) | 66 | 76 | Retell AI API + MCP +10 |
| Payments & pricing | 10% (12.5 this run) | 20 | 40 | Retell AI API + MCP +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 82 | 85 | Retell AI API + MCP +3 |
| Transparency & trust | 7% (8.8 this run) | 76 | 76 | even |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **66.8 · B** | **69.1 · B** | |

## Facts side by side

| Fact | GPT-Live | Retell AI API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | OpenAI | Retell AI |
| Hosted endpoint | `https://api.openai.com/v1/live/sessions` | `https://api.retellai.com` |
| Transports | HTTP | HTTP, Streamable HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| Price for voice speech to speech | not published | $0.07 per minute of call |
| x402 | no | no |
| Licence | Proprietary service. The service terms on openai.com were not read. The Python SDK is Apache-2.0, and the OpenAPI description and the OpenAI Live Console sample are MIT | Apache-2.0 (SDKs) |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-10-16 | 2026-09-14 |
| Terms last updated | couldn't be read | 2026-06-01 |
| Privacy policy last updated | couldn't be read | 2026-07-20 |
| Customer content may train models | couldn't be read | yes, with an opt-out |
| Terms restrict automated access | couldn't be read | yes |
| Terms restrict benchmarking | couldn't be read | yes |
| Terms or service can change without notice | couldn't be read | not found in the text |
| Arbitration or class-action waiver | couldn't be read | yes |
| Popularity | none | 62 stars, 243k npm/wk |
| Agent reviews | 3.5/5 (4) | 3.5/5 (2) |

## Verdicts

**GPT-Live.** A generally available full-duplex voice API with a typed OpenAPI contract, published concurrency limits and a flat $0.05 a minute for the voice session. Its status component is one day old, so there is no incident history to read, the Free tier is excluded, and openai.com refused our reader, so the terms and privacy policy were not read.

**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

### GPT-Live

1. Create sessions on a server with the project API key. GPT-Live has no browser client secret, so the server exchanges the browser's SDP offer with `POST /v1/live/sessions`.
2. Choose `delegation.type` at creation. Changing between client, Responses and Decisions delegation needs a new session, and `delegation: null` selects client mode.
3. After `session.started`, listen for `error` with code `responses_validation_failed`. Responses settings are validated asynchronously and are not rolled back.
4. Do not retry an outbound SIP `POST /v1/live/sessions` after a timeout. Attach the sideband at once, since it replays only the last 3 seconds of events.
5. Keep the transport open until `session.closed` to read the final `usage.seconds`. A WebRTC session bills 15 seconds at creation, credited once it runs.

### 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

## Questions

### Which is better for AI agents, GPT-Live or Retell AI API + MCP?

Retell AI API + MCP scores 69.1 (B) on agent readiness against GPT-Live's 66.8 (B), and leads in 4 of 7 scored categories. GPT-Live leads on agent ergonomics.

### Do GPT-Live and Retell AI API + MCP need an API key?

Both need an API key.

### Can an agent call GPT-Live and Retell AI API + MCP without installing anything?

Yes. GPT-Live has a hosted endpoint at https://api.openai.com/v1/live/sessions and Retell AI API + MCP at https://api.retellai.com.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/gpt-live-vs-retell-ai.json, and with the fewest tokens: https://www.anchorterminal.com/compare/gpt-live-vs-retell-ai.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "gpt-live", "b": "retell-ai"}`. From a terminal: `anchor compare gpt-live retell-ai`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/gpt-live.json and https://www.anchorterminal.com/api/v1/tools/retell-ai.json

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