AI Tool Comparison
Comparing as AI Agent BuildersSynthflow vs Retell AI
Synthflow
VS
Retell AI
Verdict by Category
Detailed Comparison
Feature
Synthflow
Retell AI
Pricing
CustomSynthflow offers a free build tier where users can design custom call flows, set up voicemail detection, and configure integrations at no upfront cost using industry templates or a from-scratch builder. Once ready to launch, usage switches to a Pay-As-You-Go model based on actual calls and chats conducted. Enterprise contracts start at $30,000 annually, with final pricing scoped around call volume, concurrency, telephony setup (Synthflow Native Telephony, SIP trunking, or approved enterprise telephony), integrations, security review (MSA/DPA support, workspace controls), and launch support including implementation, onboarding, and ongoing optimization.
FreemiumRetell AI's Pay-as-you-go plan starts at $0 with $10 in free credits, no commitments, and full platform access. AI Voice Agents cost $0.07-$0.31 per minute depending on the LLM and voice provider selected, with a base cost breakdown of $0.055/min for Retell's voice infrastructure, $0.015-$0.040/min for text-to-speech (ElevenLabs is priciest at $0.040/min), and LLM costs ranging from $0.003/min (GPT 5 nano) to $0.16/min (GPT 5.5). AI Chat Agents start at $0.002+ per message. The plan includes 20 free concurrent calls, with additional concurrency at $8/month each; the first 10 knowledge bases are free, then $8/month each; phone numbers cost $2/month and verified numbers have a one-time $10 fee. Add-ons include Knowledge Base (+$0.005/min), Batch Call (+$0.005/dial), Branded Call ID (+$0.10/outbound call), Advanced Denoising and Safety Guardrails (+$0.005/min each), PII Removal (+$0.01/min), and AI Quality Assurance ($0.10/min after 100 free minutes). The Enterprise plan offers custom pricing with dedicated stable servers, custom SSO, role-based access control, custom MSA/DPA/BAA terms, high concurrent call caps, and 24/7 support with a dedicated portal.
Categories
AI No-Code / Automation Tools
AI ChatbotsAI No-Code / Automation ToolsAI Developer APIs & PlatformsAI Audio & Music Tools
Summary
Enterprise-ready Voice AI agents for automated phone calls
Build human-like AI voice agents for phone calls with ~600ms latency
Synthflow Pros & Cons
Pros
- No-code Flow Designer makes complex voice logic accessible to non-technical teams
- In-house telephony delivers sub-100ms latency and 99.99% uptime without third-party carrier dependency
- Free tier for building and testing agents before committing to paid usage
- Strong compliance credentials (SOC 2, HIPAA, PCI DSS, GDPR, ISO 27001) for regulated industries
- Proven at scale with 65M+ monthly calls and named enterprise customers like Freshworks
Cons
- Pricing is opaque, with enterprise contracts starting around $30,000 annually rather than transparent self-serve tiers
- Deep enterprise focus (SOC 2, HIPAA, dedicated onboarding) may be more than smaller businesses need or can justify
- The free build tier still requires moving to a Pay-As-You-Go model to actually launch and take live calls
- Full value depends on enterprise telephony setup and integrations, which adds initial implementation time
- Smaller team and shorter track record (founded 2023) compared to some larger voice AI competitors
Retell AI Pros & Cons
Pros
- Industry-leading ~600ms latency for natural, fluid conversations
- True pay-as-you-go billing with no annual contracts required to start
- Highly configurable flow builder with real-time function calling
- Broad LLM and TTS provider choice, including Claude, GPT, and Gemini models
- SOC 2, HIPAA, and GDPR compliant out of the box
- Simulation testing and detailed call analytics for continuous quality improvement
Cons
- Billing continues during silence and hold time since speech recognition stays active
- Advanced voices like Elevenlabs cost more per minute than platform-native voices
- Enterprise-grade features like SSO and custom BAAs require the custom-priced Enterprise plan
- Costs can add up quickly at scale when combining premium LLMs, TTS, and add-ons like AI QA
- No native mobile app; management happens through the web dashboard