Voice Agent Platforms
Retell AI vs Synthflow: pay as you go vs a $30,000 contract
Pricing and features, side by side. Last verified October 24, 2026. Spot a wrong price? support@cozzo.io
Cozzo’s tip: start with the billing row. It’s where the surprises hide.
Cozzo’s verdict. Short answer: for most small and mid-size businesses, Retell AI. You can sign up today, pay $0.07–$0.31 a minute with no contract, and we’ve tested it on real phone calls (1.04 s median reply, 12 of 15 Round 4 receptionist calls passed). Synthflow now sells only enterprise contracts, starting at $30,000 a year, with implementation and launch support included. That floor is about $2,500 a month, which Retell’s default setup only reaches at roughly 20,000 call minutes a month. Pick Synthflow if you want a vendor to scope, build and launch a large deployment for you. We haven’t tested Synthflow, because there’s no self-serve plan to sign up for.
| Detail | Retell AI | Synthflow |
|---|---|---|
| TypeSame | BothVoice Agent Platforms | |
| Billing styleDiffers | Pay as you go | Quote only |
| Starting priceDiffers | $0 platform fee; $0.07–$0.31/min for voice agents | Enterprise contracts from $30,000/year |
| BillingDiffers | Usage-based (per minute), pay as you go | Enterprise contracts |
| HIPAA / BAADiffers | HIPAA compliant; self-serve BAA with no additional fee (Retell compliance docs) | SOC 2, HIPAA, PCI DSS and GDPR (synthflow.ai, read Oct 24, 2026); MSA/DPA and security review in the contract |
| Best forDiffers | Teams that want a no-code flow builder plus an API with itemized per-minute pricing | Businesses wanting a no-code platform on an annual enterprise contract |
| Key featuresDiffers |
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| Last verifiedSame | BothOctober 24, 2026 | |
- Retell AI: 1.04 s median reply time (tied 1 of 8, 11 calls)
- Synthflow: not tested yet
Measured on Cozzo’s test calls
- Retell AI: 1.04 s median reply time (11 phone calls); cost $0.080–0.084 per ~32 s call (about $0.15/min)
From our own phone calls on Oct 20, 2026, vendor defaults. Measured cost is what our calls cost, not a list price.
Retell AI is pay as you go: $0 platform fee, $0.07–$0.31 per call minute depending on the voice and LLM you pick, 20 concurrent calls included, $10 in free credits to start, and no minimums or contracts. A minute is built from Retell’s voice infrastructure ($0.055), a voice ($0.015 for Retell, Cartesia or OpenAI voices, up to $0.10 for ElevenLabs v3 and v4), the LLM (priced per model) and telephony ($0.015/min on a Retell number, nothing extra on your own SIP trunk). Synthflow’s pricing page lists one option: enterprise contracts from $30,000 a year, scoped around call volume, concurrency, telephony setup, integrations, security needs and launch support. It publishes no per-minute rate and no self-serve plan.
Sources: Retell AI · Synthflow
Retell AI vs Synthflow: prices and plans
Retell AI
- How you pay
- Pay as you go, $0.07–$0.31/min. No platform fee, minimums or contracts. Enterprise: custom pricing
- Getting started
- Sign up free with $10 in free credits; full platform access
- Per-minute rate
- Voice infra $0.055 + voice $0.015–$0.10 + LLM by model (e.g. GPT 5.1 $0.04, GPT 4.1 mini $0.0128) + telephony
- Telephony
- Retell numbers $2/mo and US calls $0.015/min (Twilio or Telnyx). No charge on your own SIP trunk or carrier
- Concurrent calls
- 20 free, then $8 per extra call a month. Enterprise from 50+
- Setup and support
- Self-serve with templates and simulation testing; community and email support. Enterprise adds 24/7 support and implementation help (add-on)
- Compliance
- SOC 2 Type 1 and 2, HIPAA, GDPR. BAA self-signed at no extra fee
- Billing details
- Billed per second of connected call, summed monthly; silence counts; after a transfer only telephony continues; failed calls free
- 1,000 call minutes a month
- About $110 on your own carrier, or about $127 on a Retell number, at Retell’s default calculator mix
- 5,000 call minutes a month
- About $550 on your own carrier, or about $627 on a Retell number
Synthflow
- How you pay
- Enterprise contract from $30,000 a year, scoped to call volume, concurrency, telephony, integrations, security and launch support
- Getting started
- No self-serve plan on the pricing page; you scope a contract with sales
- Per-minute rate
- Not published
- Telephony
- Synthflow’s own telephony, SIP trunking or approved enterprise telephony, scoped in the contract
- Concurrent calls
- Custom concurrency planning in the contract
- Setup and support
- Implementation, onboarding, testing, training, launch support and ongoing optimization in the contract
- Compliance
- SOC 2, HIPAA, PCI DSS and GDPR (Synthflow’s site); MSA/DPA support and security review
- Billing details
- Scoped in the contract
- 1,000 call minutes a month
- Contract floor averages $2,500 a month
- 5,000 call minutes a month
- Contract floor averages $2,500 a month
Prices read on retellai.com/pricing and synthflow.ai/pricing on Oct 24, 2026; compliance from docs.retellai.com and synthflow.ai. Retell examples use the mix its own calculator shows ($0.055 voice infra + $0.015 voice + $0.04 LLM = $0.11/min; +$0.015/min and $2/mo for a Retell number), before add-ons such as knowledge base (+$0.005/min). Your own carrier bills you separately. Our own Retell test calls on default settings came to about $0.15/min. Synthflow’s contract covers more than minutes (telephony, implementation, support), so the floor isn’t a per-minute comparison.
What Cozzo measured on real calls
Retell AI
- Reply speed (Oct 20 phone calls)
- 1.04 s median reply, 11 calls, vendor defaults
- Round 4 receptionist test (dental script)
- 12 of 15 calls passed; 1.38 s median reply (4th of 8); callback number read back correctly 0 of 3 times (1 unclear); stopped within 0.50 s when interrupted
- Round 5 (roofing & HVAC, gym, coaching)
- Passed every gym and coaching quote, booking, emergency and after-hours call; roofing: callback read-back 1 of 4, quote 0 of 2 and booking 1 of 2 (both scored with the read-back), emergency and after-hours passed; median reply 1,280–1,540 ms
- Measured cost
- $0.080–$0.084 per ~32 s call (about $0.15/min) with Retell’s default voice and LLM
Synthflow
- Reply speed (Oct 20 phone calls)
- Not tested
- Round 4 receptionist test (dental script)
- Not tested
- Round 5 (roofing & HVAC, gym, coaching)
- Not tested
- Measured cost
- Not tested
Small samples (1–3 calls per scenario per vendor), so treat close numbers as ties. Full method and limits are on each benchmark page. Synthflow sells only enterprise contracts, so we had no self-serve account to test.
Questions
Is Retell AI cheaper than Synthflow?
For almost every small or mid-size business, yes. Retell has no platform fee or minimum: at its default calculator mix ($0.11/min plus $0.015/min for a Retell number), 1,000 call minutes a month is about $127 and 5,000 about $627. Synthflow’s contracts start at $30,000 a year, about $2,500 a month, which covers implementation and support as well as calls. Retell’s default setup only reaches that much at roughly 20,000 minutes a month.
Does Synthflow still have a free plan or per-minute pricing?
Not on its pricing page as of Oct 24, 2026. Synthflow lists one option, enterprise contracts from $30,000 a year, scoped around call volume, concurrency, telephony, integrations, security needs and launch support. It doesn’t publish a per-minute rate.
Which is faster, Retell or Synthflow?
We can only answer for Retell. On Cozzo’s Oct 20 phone calls, Retell AI’s median reply was 1.04 s (11 calls, default settings), and 1.38 s in our Round 4 receptionist calls. We haven’t tested Synthflow. Synthflow says its in-house telephony runs at under 100 ms, but that’s the phone network leg, not the full time a caller waits for an answer.
Do Retell AI and Synthflow support HIPAA?
Both say so. Retell’s docs say it’s HIPAA compliant and SOC 2 Type 1 and 2 certified, with a BAA you self-sign at no extra fee before sending patient data, on pay as you go. Synthflow’s site lists SOC 2, HIPAA, PCI DSS and GDPR, with security terms handled in its enterprise contract.
Which should a small business pick?
Retell AI, or another self-serve platform, unless you have the budget and call volume for a $30,000-a-year contract. If you don’t want to build the agent yourself, compare ready-made AI receptionists, which start at a flat monthly fee, on our AI receptionist pages.