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Retell AI vs Synthflow

Two fact sheets from our own research, side by side — pricing, platforms, API access and status re-checked by us rather than quoted from the vendors.

The short answer

Entry price
Retell AI from $0.07/min, Synthflow from $30000/yr — different billing units, so no direct winner
Free plan
Retell AI has one; Synthflow prices on request
Public API
Both have one
Higher Trust score
Retell AI — 92 vs 80 for Synthflow
Best fit
Retell AI: Teams replacing an outbound qualification or booking script · Synthflow: Contact centres and BPOs automating inbound call volume

From our own records as of each tool's last check. Anything we have not confirmed is left out rather than guessed. How we verify

Retell AIBuild and run AI phone agents that book, qualify and transfer calls, billed by the minute.SynthflowEnterprise platform for building, testing and running AI voice agents that answer and place phone calls over its own telephony.

Side by side

FactRetell AISynthflow
CategoryVoice Agents & Phone AIVoice Agents & Phone AI
Pricing modelFreemiumContact
Starts at$0.07/min$30000/yr
Public APIYesYes
Trust score92 / 10080 / 100
PlatformsWeb, APIWeb, API
CompanyRetell AI Inc.Synthflow AI
Launched20232023
Last verifiedOct 15, 2026Oct 29, 2026

What our research says

Retell AI

One of the more honest voice-agent stacks: the pricing page breaks out infrastructure, TTS and LLM cost per minute so you can predict a call's cost instead of guessing. Telephony choice is wide and the concurrency allowance is generous. The catch is that per-minute billing plus add-ons makes a busy contact centre expensive fast, and the cheap end of the range only holds if you pick the cheap models.

Pros

  • Per-minute cost broken down by voice infrastructure, TTS provider and LLM on the public pricing page
  • Telephony via SIP trunking, Twilio and Vonage plus n8n, HubSpot, Make and Go High Level integrations
  • 20 concurrent calls included before any concurrency charge
  • Voice, chat and SMS agents share one platform and API
  • HIPAA path exists via a signed BAA covered in the terms of service

Cons

  • Cost per minute more than quadruples between the cheapest and most capable model combinations
  • Knowledge base, denoising, PII removal and branded caller ID are all metered extras
  • No flat-rate plan, so a spike in call volume lands straight on the invoice

Synthflow

Synthflow targets companies and BPOs that want to automate a real volume of phone calls with testing and QA around the agents. Small businesses wanting a cheap receptionist bot, or developers wanting pay-per-minute experiments, will find the $30,000 entry point too high.

Pros

  • Own telephony network as well as SIP trunking
  • Built-in simulated-call testing and automatic QA
  • Visual flow builder plus API and CRM integrations
  • Covers both voice and chat agents

Cons

  • No published self-serve plan or per-minute rate
  • Minimum annual contract of $30,000
  • Pricing depends on scoping with sales

Which one fits

Choose Retell AI if you need

  • Teams replacing an outbound qualification or booking script
  • Contact centres that already have Twilio, Vonage or SIP trunking
  • Developers who want per-minute cost visibility before launch

Choose Synthflow if you need

  • Contact centres and BPOs automating inbound call volume
  • Enterprises replacing IVR menus with conversational agents
  • Healthcare, retail and financial services teams booking appointments by phone

Retell AI vs Synthflow: the questions people ask

Is Retell AI cheaper than Synthflow?

They charge in different units, so there is no like-for-like answer: Retell AI starts at $0.07/min, Synthflow at $30000/yr. Entry price is the lowest paid plan as we last verified it.

Does Retell AI or Synthflow have a free tier?

Retell AI has a free tier; Synthflow prices on request.

Which has a public API, Retell AI or Synthflow?

Both ship a public API, so either can be built on; the fact table above shows the platforms each one runs on.

More comparisons

All Retell AI alternatives →All Synthflow alternatives →Browse all Voice Agents & Phone AI →