Head to head
Retell AI vs Synthflow
Written By Research Team
AI Outbound Calling
Fact Checked
All pricing verified against vendor documentation
Updated
Higher score
Retell AI
The most granular, itemised pricing in the category — and the easiest honest cost model to audit.
Retell publishes a full component breakdown: voice infrastructure, TTS, each LLM, and every add-on priced separately. That is unusual and genuinely pro-buyer — you can model your real cost per minute before signing anything. It is also the most generous free start, with $10 in credits and 20 concurrent calls at no cost. The trade-off is that the headline '$0.07–$0.31/min' is a wide band, and your actual rate depends entirely on which model you pick.
Synthflow
Enterprise-only voice AI with ISO 27001 and EU hosting — and a $30,000 annual floor.
Synthflow has moved upmarket and now sells enterprise contracts only, starting at $30,000 per year. To its credit it publishes that floor, which most sales-gated vendors will not do. The compliance stack is the strongest here alongside Bland — SOC 2, HIPAA, GDPR and ISO 27001, with EU or US hosting. But there is no self-serve path at all: you cannot place a test call without going through sales.
Side by side
| Criterion | Retell AI | Synthflow |
|---|---|---|
| Overall score | 84/100 | 69/100 |
| Rank | #4 | #8 |
| Type | Autonomous AI agent | Autonomous AI agent |
| Pricing model | Published | Sales-gated |
| Headline cost | $0.07–$0.31/min depending on voice and model, from $0 with $10 free credits | Enterprise contracts start at $30,000 annually |
| Concurrency | 20 free concurrent calls; additional concurrency $8/mo each | Custom concurrency planning with routing and escalation paths |
| Free trial | $10 in free credits and 20 free concurrent calls | None |
| Certifications | SOC 2 certified, HIPAA-ready, Custom SSO, Dedicated server on Enterprise | SOC 2, HIPAA, GDPR, ISO 27001, EU and US hosting options, MSA/DPA support |
Score by criterion
| Criterion | Max | Retell AI | Synthflow |
|---|---|---|---|
| Pricing transparency | 20 | 18 | 8 |
| Outbound capability | 20 | 17 | 15 |
| Compliance & security | 20 | 15 | 19 |
| Integrations & extensibility | 15 | 12 | 14 |
| Time to first call | 15 | 14 | 4 |
| Scale & reliability | 10 | 8 | 9 |