# OpenAI Realtime API vs Retell AI API + MCP (slim)

> Retell AI scores 69.1 (B) to OpenAI Realtime's 63.3 (B) for voice agents. Prices, MCP, x402, uptime and agent notes side by side.

- Full: https://www.anchorterminal.com/compare/openai-realtime-vs-retell-ai.md (~2,600 tokens) · this version ~730 tokens · JSON https://www.anchorterminal.com/compare/openai-realtime-vs-retell-ai.json · canonical https://www.anchorterminal.com/compare/openai-realtime-vs-retell-ai
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · Updated: 2026-10-09

Retell AI API + MCP scores 69.1 (B) on agent readiness against OpenAI Realtime API's 63.3 (B), and leads in 5 of 7 scored categories. OpenAI Realtime API leads on reliability and agent ergonomics. Both do voice agents.

- OpenAI Realtime API: B 63.3, rank #400 of 950 · https://www.anchorterminal.com/tools/openai-realtime.min.md
- Retell AI API + MCP: B 69.1, rank #196 of 950 · https://www.anchorterminal.com/tools/retell-ai.min.md
- OpenAI Realtime API, good for Teams building their own voice agent on one speech-to-speech model who want browser, server and phone transports from one vendor and can run a backend for secrets and tools. Ahead on Reliability, 67 against 60; Agent ergonomics, 76 against 60.
- Retell AI API + MCP, 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 84; Security & auth, 76 against 61; Payments & pricing, 40 against 20; Maintenance & community, 85 against 52; Transparency & trust, 76 against 71. Also Free to start without a card.

| Category | OpenAI Realtime API | Retell AI API + MCP |
| --- | --- | --- |
| Reliability (16%) | 67 | 60 |
| Performance (10%) | pending | pending |
| Schema & documentation (13%) | 84 | 92 |
| Agent ergonomics (13%) | 76 | 60 |
| Security & auth (14%) | 61 | 76 |
| Payments & pricing (10%) | 20 | 40 |
| Task success (10%) | pending | pending |
| Maintenance & community (7%) | 52 | 85 |
| Transparency & trust (7%) | 71 | 76 |

| Fact (where they differ) | OpenAI Realtime API | Retell AI API + MCP |
| --- | --- | --- |
| Vendor | OpenAI | Retell AI |
| Hosted endpoint | `https://api.openai.com/v1/realtime` | `https://api.retellai.com` |
| Transports | HTTP | HTTP, Streamable HTTP |
| Licence | Proprietary service. The service terms on openai.com were not read. The Agents SDK for TypeScript and the OpenAPI description are MIT | Apache-2.0 (SDKs) |
| Last release | 2026-07-28 | 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 | none | 3.5/5 (2) |