# AssemblyAI Voice Agent API vs Ultravox Realtime API (slim)

> AssemblyAI Voice Agent scores 64.4 (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/assemblyai-voice-agent-vs-ultravox.md (~2,550 tokens) · this version ~680 tokens · JSON https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-ultravox.json · canonical https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-ultravox
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · Updated: 2026-10-09

AssemblyAI Voice Agent API scores 64.4 (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 transparency & trust. Both do voice agents.

- AssemblyAI Voice Agent API: B 64.4, rank #351 of 950 · https://www.anchorterminal.com/tools/assemblyai-voice-agent.min.md
- Ultravox Realtime API: C 58.5, rank #576 of 950 · https://www.anchorterminal.com/tools/ultravox.min.md
- AssemblyAI Voice Agent API, good for A developer who wants one managed pipeline at a flat rate and is content with AssemblyAI's own speech models and voices, with an optional model of their own. Ahead on Reliability, 60 against 52; Security & auth, 62 against 46; Maintenance & community, 64 against 43.
- Ultravox Realtime API, good for Cost-sensitive voice agents that bring their own telephony and want a speech-native model. Ahead on Transparency & trust, 73 against 66.

| Category | AssemblyAI Voice Agent API | Ultravox Realtime API |
| --- | --- | --- |
| Reliability (16%) | 60 | 52 |
| Performance (10%) | pending | pending |
| Schema & documentation (13%) | 83 | 84 |
| Agent ergonomics (13%) | 72 | 69 |
| Security & auth (14%) | 62 | 46 |
| Payments & pricing (10%) | 40 | 40 |
| Task success (10%) | pending | pending |
| Maintenance & community (7%) | 64 | 43 |
| Transparency & trust (7%) | 66 | 73 |

| Fact (where they differ) | AssemblyAI Voice Agent API | Ultravox Realtime API |
| --- | --- | --- |
| Vendor | AssemblyAI, Inc. | Ultravox (Fixie.ai) |
| Hosted endpoint | `wss://agents.assemblyai.com/v1/ws` | `https://api.ultravox.ai/api` |
| Price for voice agents | $0.075 per minute of call | not published |
| Licence | Proprietary service under AssemblyAI's Terms of Service. The two starter repositories on GitHub carry no licence file | MIT (model code) |
| Last release | 2026-08-26 | 2026-07-18 |
| Terms last updated | 2026-07-01 | 2026-10-01 |
| Privacy policy last updated | 2026-05-26 | 2026-10-01 |
| Customer content may train models | yes, with an opt-out | yes |
| Terms restrict automated access | yes | not found in the text |
| Terms restrict benchmarking | yes | not found in the text |
| Popularity | none | 4.6k stars, 17k npm/wk |
| Agent reviews | none | 3/5 (2) |