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Retell AI vs Synthflow: which voice AI platform fits your team?

Updated 28 October 2026 · 4 min read

Short answer

Pick Retell AI if you want published per-minute rates ($0.07–$0.31/minute), a $10 free credit to start, and no annual contract. Pick Synthflow if you're an enterprise team with a $30,000+ annual budget that needs named contact-center integrations like Cisco, Avaya, and Genesys.

Retell AI publishes $0.07–$0.31/minute rates with no contract; Synthflow's only published price is $30,000 annually for enterprise.
300 three-minute calls cost $63–$279 on Retell AI; a Synthflow bill is not computable from published rates.
Synthflow names Cisco, Avaya, Genesys, and RingCentral integrations; Retell AI offers more channels including web chat and in-app.
Both claim HIPAA and SOC 2; Retell AI adds ISO 27001, Synthflow adds PCI DSS.

Retell AI and Synthflow, side by side

Published facts only. Where a vendor does not say, we print “Not stated”.

Retell AI

Type: Voice agent platform
Bills by: Per minute
Entry price: $0.07-$0.31/minute
300 calls a month: $63–$279
Free way to try: $10 in free credits at signup with full platform access and no contract, plus 20 free concurrent calls

Phone: listed
Web chat: listed
Email: not listed
SMS: listed
WhatsApp: not listed
Social DMs: not listed
In-app: listed

Synthflow

Type: Voice agent platform
Bills by: Quote only
Entry price: $30,000 annually
300 calls a month: Not modelled
Free way to try: Free to start and build an AI agent; pay-as-you-go billing begins when you launch and pay only for actual calls and chats conducted.

Phone: listed
Web chat: not listed
Email: not listed
SMS: listed
WhatsApp: listed
Social DMs: not listed
In-app: not listed

Source: each vendor’s product and pricing pages, checked 28 October 2026. Bill estimate: 300 calls of 3 minutes on the cheapest published plan.

Retell AI vs Synthflow at a glance

These two platforms overlap on paper: both build AI voice agents for phone automation, both are developer-led setups, and both claim HIPAA and SOC 2 compliance. The split is commercial. Retell AI publishes its rates and lets you start with $10 in free credits (Retell AI pricing). Synthflow publishes one enterprise tier starting at $30,000 annually and scopes everything else through sales (Synthflow pricing).

	Retell AI	Synthflow
What it is	Platform for building and deploying AI voice agents	Enterprise voice AI platform for automating phone calls
Who sets it up	Developer	Developer
Billing unit	Per minute	Quote-only
Entry price	$0.07–$0.31/minute	$30,000 annually
Per-unit price	$0.07–$0.31/minute published	Not published
Free option	$10 in free credits, full platform access, 20 free concurrent calls	Free to build an agent; pay-as-you-go billing starts at launch
Channels	Phone, web chat, SMS, in-app	Phone, SMS, WhatsApp
Handoff	AI briefs the human agent, confirms readiness, fee stops after transfer	Built-in handoff with triggers based on failed attempts or sentiment
Booking	Checks availability and books directly	Appointment booking, demos, viewings, reminders, follow-ups
Compliance	HIPAA, SOC 2 Type II, GDPR, ISO 27001	SOC 2, HIPAA, PCI DSS, GDPR
Integrations listed	10 (Twilio, Telnyx, HubSpot, Make, n8n, ElevenLabs, OpenAI, others)	13 (Cisco, Avaya, Genesys, RingCentral, Salesforce, HubSpot, others)

Full profiles: Retell AI and Synthflow.

Same 300 calls, two bills

We can only compute one side of this. Retell AI publishes a $0.07–$0.31 per-minute range depending on the voice, model, and telephony you choose. Synthflow does not publish a per-minute or per-call rate anywhere in the material we reviewed, so a Synthflow bill for any call volume is not computable without a sales conversation.

Using a 3-minute average call, 300 calls is 900 minutes:

Retell AI at $0.07/minute: $63
Retell AI at $0.31/minute: $279
Synthflow: not computable from published rates; enterprise contracts start at $30,000 annually, and pay-as-you-go rates for calls and chats are not stated

At 1,000 calls (3,000 minutes), Retell AI lands between $210 and $930. For Synthflow, the only published anchor is the $30,000 annual enterprise floor.

Retell AI's range is wide because the rate depends on your LLM, text-to-speech voice, and add-ons. Watch the extras: branded call ID adds $0.10 per outbound call, concurrent calls beyond the 20 free ones cost $8 per call per month, and knowledge bases beyond the first 10 cost $8 per KB per month. Billing also continues during silence and hold time, because the speech-to-text engine stays active. On the plus side, billing is per-second with no rounding up, failed calls are not charged, and the AI agent fee stops once a call transfers to a human.

For a broader cost view across vendors, see our AI receptionist cost guide and the AI call center savings calculator.

Where is Retell AI stronger?

Published pricing. The $0.07–$0.31 per-minute range is on the site, with per-second billing and no rounding up per call. You can model your cost before talking to anyone. Synthflow's total cost depends on scoping factors like call volume, concurrency, and telephony setup, so it stays unclear until sales scopes it.

Low-friction start. $10 in free credits at signup, full platform access, 20 free concurrent calls, no contract. You can build and run real calls today.

Compliance depth on paper. HIPAA, SOC 2 Type II, GDPR, and ISO 27001 are stated on the site. Synthflow lists SOC 2, HIPAA, PCI DSS, and GDPR — it adds PCI DSS but does not list ISO 27001.

Channel breadth. Phone, web chat, SMS, and in-app. Chat agents start at $0.002 per message. Synthflow lists phone, SMS, and WhatsApp.

Transfer economics. Once a call hands off to a human, the AI voice agent fee stops and only the telephony fee continues.

Where is Synthflow stronger?

Contact-center integrations. Synthflow names Cisco, Avaya, Genesys, RingCentral, Freshcaller, Freshdesk, Freshservice, Salesforce, HubSpot, Cal.com, GoHighLevel, Zapier, and Google Cloud. If you run an existing contact center on Cisco or Genesys, that list matters. Retell AI's integrations skew toward telephony and builder tooling: Twilio, Telnyx, Vonage, SIP trunking, Make, n8n, ElevenLabs, OpenAI, HubSpot, Go High Level.

Telephony infrastructure. Synthflow claims an in-house telephony network with sub-100 ms latency and 99.99% uptime, plus SIP/PBX compatibility. Retell AI relies on telephony partners like Twilio and Telnyx alongside SIP trunking.

Enterprise packaging. The enterprise tier includes an SLA, native telephony or SIP trunking, custom concurrency, security review, and implementation and launch support. Retell AI's enterprise plan offers dedicated implementation support and a dedicated stable server, but both are add-ons.

Handoff controls. Handoff triggers can be controlled based on failed attempts or sentiment, and agents can transfer urgent calls to the right team.

WhatsApp. Synthflow lists WhatsApp as a channel; Retell AI does not.

Who should pick which?

Pick Retell AI if:

You want published per-minute rates and no annual contract or minimum commitment
You're a developer or have one, and want to start with $10 in free credits today
You need HIPAA, SOC 2 Type II, GDPR, or ISO 27001 stated for a regulated industry like healthcare, insurance, or financial services
You want web chat and in-app channels alongside phone
Predictable per-second billing matters more than a managed enterprise rollout

Pick Synthflow if:

You're an enterprise or BPO with a $30,000+ annual budget for voice AI
You run Cisco, Avaya, Genesys, or RingCentral and need named integrations
You want an SLA, custom concurrency, security review, and launch support bundled in
PCI DSS is on your compliance checklist
You need WhatsApp as a channel

Skip Retell AI if you need a flat monthly subscription or a fully managed service where the vendor handles setup and ongoing changes. Skip Synthflow if you're a small business that needs transparent, low-cost pricing or a published per-minute rate.

If neither fits, browse the voice agent platform directory or get matched with a shortlist.

Questions buyers ask

Is Retell AI cheaper than Synthflow?

On published numbers, yes at low volume. Retell AI charges $0.07–$0.31 per minute with no contract, so 300 three-minute calls cost $63–$279. Synthflow's only published price is enterprise contracts starting at $30,000 annually, and its pay-as-you-go rates are not stated, so a direct comparison at scale isn't possible.

Does Synthflow have a free trial?

Synthflow lets you build an AI agent free with templates. Pay-as-you-go billing begins when you launch, and you pay only for actual calls and chats conducted. The per-call or per-minute rates under that model are not published, so the cost of a test launch is unclear upfront.

Which is better for healthcare, Retell AI or Synthflow?

Both list HIPAA compliance. Retell AI also states SOC 2 Type II, GDPR, and ISO 27001, and lists healthcare among its industries. Synthflow adds PCI DSS alongside SOC 2, HIPAA, and GDPR, and also targets healthcare. The deciding factor is usually budget: published per-minute rates versus a $30,000 annual enterprise floor.

Do Retell AI and Synthflow require a developer?

Both are developer-led setups. Retell AI provides pre-built agent templates, webhooks, and API access on its pay-as-you-go plan. Synthflow's enterprise tier includes implementation and launch support, which offloads some work, but the platform is aimed at operations and engineering teams.

Can either platform replace a human receptionist?

Both automate phone answering, booking, and routing, and both hand off to humans when needed. Retell AI stops its AI agent fee after transfer; Synthflow controls handoff triggers by failed attempts or sentiment. For a human-service comparison, see our guide on AI receptionists versus answering services.

What happens to costs as call volume grows?

Retell AI scales linearly: 1,000 three-minute calls cost $210–$930 at published rates, plus add-ons like $8 per concurrent call beyond the 20 free. Synthflow's enterprise pricing is scoped around call volume, concurrency, and telephony setup, so growth costs require a sales conversation.