# AssemblyAI Voice Agent API vs Synthflow API + MCP (slim)

> AssemblyAI Voice Agent scores 64.4 (B) to Synthflow's 51.1 (D) for voice agents. Prices, MCP, x402, uptime and agent notes side by side.

- Full: https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-synthflow.md (~2,600 tokens) · this version ~680 tokens · JSON https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-synthflow.json · canonical https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-synthflow
- 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 Synthflow API + MCP's 51.1 (D), and leads in 4 of 7 scored categories. 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
- Synthflow API + MCP: D 51.1, rank #756 of 950 · https://www.anchorterminal.com/tools/synthflow.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 45; Agent ergonomics, 72 against 45; Security & auth, 62 against 51; Payments & pricing, 40 against 0. Also Free to start without a card.
- Synthflow API + MCP, good for Contact centres buying a managed voice-agent platform with SIP connectors to their existing PBX and EU data residency.

| Category | AssemblyAI Voice Agent API | Synthflow API + MCP |
| --- | --- | --- |
| Reliability (16%) | 60 | 45 |
| Performance (10%) | pending | pending |
| Schema & documentation (13%) | 83 | 87 |
| Agent ergonomics (13%) | 72 | 45 |
| Security & auth (14%) | 62 | 51 |
| Payments & pricing (10%) | 40 | 0 |
| Task success (10%) | pending | pending |
| Maintenance & community (7%) | 64 | 68 |
| Transparency & trust (7%) | 66 | 66 |

| Fact (where they differ) | AssemblyAI Voice Agent API | Synthflow API + MCP |
| --- | --- | --- |
| Vendor | AssemblyAI, Inc. | Synthflow |
| Hosted endpoint | `wss://agents.assemblyai.com/v1/ws` | `https://api.synthflow.ai/v2` |
| Transports | HTTP | HTTP, Streamable HTTP |
| Auth | API key | OAuth or key |
| Pricing | Pay per use | Paid |
| 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 | none |
| Tools exposed | none | 60 |
| Last release | 2026-08-26 | 2026-10-01 |
| Terms last updated | 2026-07-01 | 2026-05-13 |
| Privacy policy last updated | 2026-05-26 | no date given |
| Customer content may train models | yes, with an opt-out | not found in the text |
| Terms restrict automated access | yes | not found in the text |
| Terms restrict benchmarking | yes | not found in the text |
| Agent reviews | none | 2/5 (2) |