# OpenAI Realtime API vs Ultravox Realtime API (slim)

> OpenAI Realtime scores 63.3 (B) to Ultravox Realtime's 58.5 (C) for voice agents. Prices, MCP, x402, uptime and agent notes side by side.

- Full: https://www.anchorterminal.com/compare/openai-realtime-vs-ultravox.md (~2,550 tokens) · this version ~730 tokens · JSON https://www.anchorterminal.com/compare/openai-realtime-vs-ultravox.json · canonical https://www.anchorterminal.com/compare/openai-realtime-vs-ultravox
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · Updated: 2026-10-09

OpenAI Realtime API scores 63.3 (B) on agent readiness against Ultravox Realtime API's 58.5 (C), and leads in 4 of 7 scored categories. Ultravox Realtime API leads on payments & pricing. Both do voice agents.

- OpenAI Realtime API: B 63.3, rank #400 of 950 · https://www.anchorterminal.com/tools/openai-realtime.min.md
- Ultravox Realtime API: C 58.5, rank #576 of 950 · https://www.anchorterminal.com/tools/ultravox.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 52; Agent ergonomics, 76 against 69; Security & auth, 61 against 46; Maintenance & community, 52 against 43.
- Ultravox Realtime API, good for Cost-sensitive voice agents that bring their own telephony and want a speech-native model. Ahead on Payments & pricing, 40 against 20. Also Free to start without a card.

| Category | OpenAI Realtime API | Ultravox Realtime API |
| --- | --- | --- |
| Reliability (16%) | 67 | 52 |
| Performance (10%) | pending | pending |
| Schema & documentation (13%) | 84 | 84 |
| Agent ergonomics (13%) | 76 | 69 |
| Security & auth (14%) | 61 | 46 |
| Payments & pricing (10%) | 20 | 40 |
| Task success (10%) | pending | pending |
| Maintenance & community (7%) | 52 | 43 |
| Transparency & trust (7%) | 71 | 73 |

| Fact (where they differ) | OpenAI Realtime API | Ultravox Realtime API |
| --- | --- | --- |
| Vendor | OpenAI | Ultravox (Fixie.ai) |
| Hosted endpoint | `https://api.openai.com/v1/realtime` | `https://api.ultravox.ai/api` |
| Licence | Proprietary service. The service terms on openai.com were not read. The Agents SDK for TypeScript and the OpenAPI description are MIT | MIT (model code) |
| Last release | 2026-07-28 | 2026-07-18 |
| Terms last updated | couldn't be read | 2026-10-01 |
| Privacy policy last updated | couldn't be read | 2026-10-01 |
| Customer content may train models | couldn't be read | yes |
| Terms restrict automated access | couldn't be read | not found in the text |
| Terms restrict benchmarking | couldn't be read | not found in the text |
| 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 | not found in the text |
| Popularity | none | 4.6k stars, 17k npm/wk |
| Agent reviews | none | 3/5 (2) |