Retell AI
VS Synthflow
Data as of October 2026Which is better, Retell AI or Synthflow?
It depends on how you want to buy and build. Synthflow suits enterprises that want a vendor-led rollout. As of October 2026, it sells annual contracts starting at $30,000. Its Enterprise package lists onboarding and launch support. It also offers a visual Flow Designer and its own telephony. New workspaces can keep data and processing fully in the US or the EU. Retell suits teams that want to build and launch without a sales contract. As of October 2026, pay as you go pricing starts at $0.07 per minute, with $10 in free credits. You can choose GPT, Claude or Gemini, or connect your own LLM. Retell does not currently run services inside the EU.
Chat Platform vs Voice Agent Platform
No-code platforms are brilliant at speed. Give Synthflow a simple use case and a small team, and you'll be running calls in a weekend.
The trade-off
Synthflow and Retell are bought in different ways. As of October 2026, Synthflow is sales-led. New customers sign an annual Enterprise contract. That contract also unlocks GPT models, campaigns and SIP trunking. Retell is self-serve. You can sign up, build and run production calls on pay as you go. Enterprise adds custom terms, SSO and dedicated support. Synthflow offers EU data hosting, which Retell does not.
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Retell is voice AI that scales with you. Low-code workflows give you developer-level control without the complexity, plus enterprise features, like warm transfer, batch calling, analytics, and compliance, all built in. Give it a job like "qualify inbound leads" and it runs the call.
- Custom LLMs and database integration, not just prebuilt flows
- Warm transfer, batch calling, and SIP trunking included
- Post-call analytics and simulation testing built in
- HIPAA, SOC 2, GDPR, and ISO 27001 on every plan
You start with a call. Retell helps you finish with a production deployment at scale.
Why Retell is Different
An agent that scales, not one you outgrow.
Easy to build. Hard to outgrow.
Synthflow's no-code builder is fast to launch, but limits you to prebuilt flows, without custom LLMs, database integration, or workflow depth. Retell's low-code approach delivers developer-level control without requiring a development team, so your agents evolve as your use cases do. Flexibility that grows with you, not a ceiling you outgrow.
Sub-Second Latency with Dynamic Turn-Taking
Synthflow follows predictable interaction steps that work well in chat but feel stiff on a call. Retell adapts to how humans actually speak—pauses, interruptions, and half-finished sentences. Conversation that flows, instead of conversation that waits.
Enterprise Call Features, Built In
Synthflow’s no-code setup can fall short for real-world call workflows—missing things like warm transfers, batch calling, branded calls, and SIP support. Retell includes all of this out of the box, plus verified phone numbers to help more customers actually pick up. Production-grade telephony is a feature, not a roadmap item.
Post-Call Analytics and Simulation Testing
Synthflow doesn't offer post-call analytics or simulation testing, so optimizing agents at scale becomes guesswork. Retell processes every call through post-call analysis, such as action items, summaries, outcomes, sentiment, and it lets you simulate calls to catch issues before they ship. Measure what's working, then make it better.
Pricing That Stays Flat as You Scale
Synthflow's per-minute rates start at $0.18–$0.22 and climb higher after monthly minute limits. Retell starts at $0.07 per minute with no platform fees, $2/month phone numbers and $5/month toll-free. Your voice AI bill shouldn't grow faster than your call volume.
Overview
Feature, Pricing & Compliance Breakdown
Synthflow's no-code builder is fast to launch but hits a ceiling on customization and analytics. Retell scales further—with custom LLM support, post-call analysis, lower per-minute rates, and automatic PII redaction included.
| Features |  | .avif) |
|---|---|---|
| Core Approach | Low-code platform built to scale | No-code builder for quick prototypes |
| Custom LLM Integration | Supported | Synthflow LLM; GPT on Enterprise; no custom endpoints |
| Warm Transfer & Batch Calling | Included | Warm transfer; campaigns on Enterprise |
| Post-Call Analytics | Real-time insights & dashboards built in | Analytics dashboard, extractors, custom evaluations |
| Simulation Testing | Included | Test Center simulations |
| Best for | Teams scaling voice AI past the prototype | Enterprises that want a scoped, vendor-led rollout |
| Batch Calling | Built to run outbound call campaigns at scale | Campaigns via API on Enterprise plans |
| Pricing | | |
|---|---|---|
| Voice AI | From $0.07/min, as of October 2026 | Annual Enterprise contracts from $30,000; no public per-minute rate, as of October 2026 |
| Phone Number | $2.00/month | Included |
| Toll Phone Number | $5.00/month | Not Supported |
| Verified Phone Number | $10/month + $10 one-time setup | Included |
| Branded Calls | $0.10 per outbound call | Limited |
| Batch Calls | $0.005 per dial | Campaigns on Enterprise plans; priced per contract, as of October 2026 |
| Extra Knowledge Base Slots | 10 free, then $8/month each | Limited |
| Concurrency Add-on | 20 free; $8/month per additional slot | Limited |
| Speech-to-Text | Included at no extra cost | Included |
Built for Contact Centers, Not Demos
Retell is the AI Voice Platform Enterprise Contact Centers Run On
Retell lets you build, test and deploy AI phone agents that handle real call volume, so your team spends its time on the conversations that need a person.
More than a no-code builder
A voice platform built to scale.
Knowledge Base Integration
Retell's Knowledge Base lets agents get accurate answers from your docs, databases, and systems, resulting in sharper responses even across long, multi-turn conversations. Synthflow's agents rely primarily on LLM memory, which breaks down once conversations get complex.
Smart Info Capture
Retell reliably captures key details mid-call (account IDs, budgets, names, preferences) and recalls them later in the conversation or hands them off to your CRM. Synthflow lacks comparable structured capture, which leads to fragile memory and inconsistent multi-turn flows.
Branded Caller ID & Verified Numbers
Retell boosts answer rates with branded caller ID and verified phone numbers, reducing the chance of calls being flagged as spam. Synthflow doesn't offer these deliverability features, leaving outbound volume exposed to missed connections.
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Concurrency on Demand
Retell includes 20 concurrent calls on every account and adds capacity on demand at $8 per concurrent call per month, with custom concurrency on Enterprise. Synthflow imposes practical concurrency caps (10 to 100+ depending on plan), with higher performance gated behind higher tiers.
Automatic PII Redaction & Access Control
Retell automatically redacts names, addresses, DOBs, passwords, and PINs from every transcript and recording, with role-based access control included on every plan. Synthflow also offers PII redaction and three workspace roles.
When to Use Each Tool
Use Synthflow when you:
- Are a small team experimenting with no-code voice agents
- Need a quick prototype without engineering support
- Run short, predictable call flows that fit prebuilt templates
- Care more about setup speed than scaling long-term
Synthflow does well when you want a vendor-led rollout under one contract.
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Use Retell when you:
- Need voice AI that scales past the prototype
- Want custom LLMs, warm transfer, and batch calling built in
- Rely on post-call analytics to prove what's working
- Care about per-minute costs that stay flat as volume grows
Retell excels when the call has to work, and keep working as you scale.
FAQ
Common Questions
How fast can I launch a voice agent with Retell?
Fast. Retell's low-code builder lets teams launch a working voice agent in under three minutes for simple use cases, with more complex workflows typically live within a few hours to a few days. You get $10 of free usage when you sign up, so you can test end-to-end calls before committing to a plan.
Does Retell require a full engineering team?
No. Most teams need one engineer for initial setup and integrations, but ongoing work — building flows, tuning prompts, adding knowledge base content — is handled by product managers, CX leads, or ops teams through the dashboard. The low-code approach gives you developer-level control without requiring a development team to run it.
Can I use custom LLMs or bring my own model?
Yes. Retell is LLM-agnostic and supports custom LLM integration through the API. Pick GPT, Claude, Gemini, an open-source model, or your own fine-tune, and swap between them as better models ship without rebuilding your workflows.
What LLMs can we use inside Retell?
Retell is LLM-agnostic. You pick the model—GPT, Claude, Gemini, open-source, or your own fine-tune—tune the prompt, and wire in your tools through an API-first stack. Model selection stays your decision, not the platform's.
How does Retell's pricing work as call volume grows?
Pay as you go from $0.07 per minute, with no platform fees and no monthly minimums; the rate depends on the LLM, voice and telephony you choose. Phone numbers are $2/month standard or $5/month toll-free. Enterprise plans offer custom pricing and concurrency, and every rate is published on the pricing page.
What analytics and testing tools does Retell include?
Every call runs through post-call analysis automatically — action items, summaries, outcomes, and sentiment — surfaced in real-time dashboards. You also get call-level transcripts, performance metrics, and simulation testing so you can tune agents before they go live instead of tuning on real customers.
Does Retell support multiple languages and international calls?
Yes. Retell supports 55 languages, along with international calling at published per-minute rates. You can run the same voice agent for customers worldwide without switching platforms, models, or pricing structures.
What security and compliance coverage does Retell include?
HIPAA, SOC 2 Type 1 & 2, GDPR, and ISO 27001 are included on every plan, not gated behind enterprise tiers. Retell also maintains greater than 99.9% uptime and offers PII redaction on every transcript and recording, with custom role-based access control on Enterprise.
Revolutionize your call operation with Retell
