Retell vs Synthflow — AI voice agent cost at your call volume
Retell vs Synthflow pricing: pay-per-minute self-service API vs a $30,000 annual enterprise contract. Cost model and buyer fit.
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Pricing verified 2026-08-25 · updated 2026-07-20→ Run the full cost calculator for your exact volume
Quick answer
At ~10,000 units/mo, Retell AI costs about $1,100/mo vs $2,500/mo for Synthflow AI (entry verified tiers; see assumptions).
Best overall value score: Retell AI (4.6/5). Easiest to start: Synthflow AI (4.6/5 ease).
Cost at 1k / 10k / 50k
| Volume / mo | RRetell AI | SSynthflow AI |
|---|---|---|
| 1,000 | $110/mo · Pay as you go | $2,500/mo · Enterprise per month equivalent of the $30,000 annual Enterprise contract minimum |
| 10,000 | $1,100/mo · Pay as you go (scaled) Extrapolated from 1,000 units @ $110/mo |
$2,500/mo · Enterprise per month equivalent of the $30,000 annual Enterprise contract minimum |
| 50,000 | $5,500/mo · Pay as you go (scaled) Extrapolated from 1,000 units @ $110/mo |
$2,500/mo · Enterprise per month equivalent of the $30,000 annual Enterprise contract minimum |
Estimates use verified list prices; confirm current checkout on vendor sites. Prices verified from vendor pages in our pricing index.
3-year TCO (at 10,000 units/mo)
| RRetell AI | SSynthflow AI | |
|---|---|---|
| Monthly (est.) | $1,100 | $2,500 |
| 3-year total | $39,600 | $90,000 |
Retell AI saves about $50,400 over 3 years at this volume (list price only).
Estimates use verified list prices; confirm current checkout on vendor sites.
At a glance
| RRetell AI | SSynthflow AI | |
|---|---|---|
| Overall score | 4.17/5 | 4.22/5 |
| Starting price | $0/mo | $2500/mo |
| Pricing basis | pay as you go, $0.07-$0.31 per minute for AI Voice Agents | per month equivalent of the $30,000 annual Enterprise contract minimum |
| Free plan | Yes | No |
| Trial | 0 days | 0 days |
| Integrations | 20+ | 200+ |
| Best for | Teams that want full control of an AI phone agent (API-first) and pure usage-based pricing with no monthly seat fee | Non-technical teams and agencies that want a drag-and-drop AI phone agent with CRM integrations out of the box |
| Retell AI review → | Synthflow AI review → |
Winner by use case
- Tightest budget: Retell AI — entry plan is $2500/mo cheaper ($30000/year at entry tier).
- Fastest to learn: Synthflow AI (4.6/5 ease of use).
- Most capability: Retell AI (4.5/5 feature depth).
- Best value overall: Retell AI (4.6/5 value score).
Feature matrix
| RRetell AI | SSynthflow AI | |
|---|---|---|
| Free plan | ✓ | ✕ |
| Trial days | 0 | 0 |
| AI features | 4 | 4 |
| Integrations | 20+ | 200+ |
| Ease of use | 3.6/5 | 4.6/5 |
| Feature depth | 4.5/5 | 4.2/5 |
| Value for money | 4.6/5 | 3.9/5 |
| Support | 4.0/5 | 4.2/5 |
Pricing, side by side
RRetell AI
| Plan | Price |
|---|---|
| Free credit | Free / custom |
| Pay as you go | $110/mo |
| Enterprise | Free / custom |
Verified 2026-08-25 · Pricing source
Strengths and weaknesses
RRetell AI
- Cheapest entry: pay only for minutes used, $10 free credit
- Transparent per-minute cost breakdown on pricing page
- Scales from prototype to thousands of concurrent calls
- Strong developer docs and API
- No visual no-code builder - assumes technical setup
- LLM and telephony costs billed on top of voice engine
- No bundled CRM or campaign UI like Synthflow
- Per-minute cost varies with chosen voice/LLM combo
SSynthflow AI
- Fastest path from zero to working phone agent - no dev needed
- Predictable monthly bill with included minutes
- Agency white-label program
- Strong template library for common use cases
- Entry plan's 50 minutes is only enough for testing
- Per-minute cost above included bundle is high on Starter
- Less flexible than API-first rivals for custom logic
- No free plan - trial only
Our verdict
The core difference is now procurement, not only who builds the agent. Retell remains a self-service, usage-priced platform for teams that can wire an API. Synthflow's public offer is enterprise-only: its pricing page says contracts start at $30,000 annually and scopes the final quote around volume, concurrency, telephony, integrations, security and launch support.
The pricing math that actually matters
- Retell lists $0.07–$0.31 per minute for AI Voice Agents, depending on the voice, LLM, telephony and add-ons. Its calculator currently shows about $0.11/min for one common configuration, so 500 minutes is roughly $55 before configuration changes.
- Synthflow has no public self-service or bundled-minute tier now. The published floor is $30,000 per year, equivalent to $2,500/month before any scope-dependent uplift.
- There is no honest public crossover calculation anymore. Retell exposes usage components; Synthflow requires a quote. Compare the Synthflow proposal against the same Retell call mix, concurrency and implementation labor rather than treating the contract minimum as an all-in per-minute rate.
Run your own volume in the AI voice agent cost calculator — it also shows the human-receptionist baseline.
Best for small businesses without a developer
Synthflow. The visual flow builder, calendar booking and CRM integrations (HubSpot, GoHighLevel) mean a working phone agent in an afternoon. Retell's docs are excellent, but "excellent docs" still means someone reads docs.
Best for agencies and technical teams
Retell for self-service and cost transparency. API-first design, bring-your-own components, batch outbound and published per-minute inputs make it the practical starting point for a technical team. Synthflow belongs on an enterprise shortlist when managed implementation, security review and contractual support justify a five-figure annual commitment.
Hidden costs and limits
- Retell: LLM and telephony are billed on top of the voice engine — the advertised per-minute number is not the whole bill. Budget the all-in figure (~$0.11/min typical).
- Synthflow: the public $30,000 annual figure is only a contract floor, not a complete quote or a guaranteed minute allowance.
- Both: phone numbers, concurrent-call limits and compliance features (HIPAA, SOC2) sit in higher tiers or add-ons.
When to choose neither
If your call volume is under ~100 minutes/month, an answering service or a plain voicemail-to-WhatsApp flow (see the lead follow-up stack) solves the problem for less. If you need deep customization of every pipeline stage, Vapi's provider-agnostic stack is the third option — currently without an open affiliate program, which is exactly why you won't see us push it harder than the data supports.
Choose Retell if someone technical owns the project and you want usage-based billing with room to customize. Choose Synthflow if you are buying an enterprise rollout with sales-assisted scoping, governance and launch support — not a low-cost no-code experiment.
Pricing sources
- Retell AI pricing — verified 2026-08-25
- Synthflow pricing — verified 2026-08-25
FAQ
Is Retell AI cheaper than Synthflow AI?
Yes. Retell AI starts at $0/mo versus $2500/mo for Synthflow AI (pay as you go, $0.07-$0.31 per minute for AI Voice Agents). Over a year that is a $30000 difference at entry tier.
Does Synthflow AI have a free plan?
No. Synthflow AI offers a 0-day trial instead. Retell AI does have a free plan, which makes it easier to test long-term before paying.
Which is easier to use, Retell AI or Synthflow AI?
Based on our scoring, Synthflow AI is easier to get started with (ease-of-use 4.6/5 vs 3.6/5).
Which has more features, Retell AI or Synthflow AI?
Retell AI scores higher on feature depth (4.5/5). Key differentiators: Usage-based pricing - no monthly platform fee; API-first: build agents programmatically; Sub-second latency voice pipeline.
What is the 3-year TCO of Retell AI vs Synthflow AI?
At ~10,000 units/mo on verified tiers, Retell AI is about $39,600 over 3 years ($1,100/mo) versus Synthflow AI at $90,000 ($2,500/mo). Retell AI saves roughly $50,400 across 3 years before add-ons. Estimates use verified list prices; confirm current checkout on vendor sites.
Full reviews: Retell AI review · Synthflow AI review
Run the numbers: cost calculator · pricing index