CentriWebIn Retell AI vs Synthflow, the bigger difference as at November 2026 is how you buy, more than how you build. Retell is pay as you go per minute with a no-code studio and an API, while Synthflow’s pricing page says every new deployment starts on an annual enterprise agreement, with no free plan, no trial and no per-minute rate.
Both now offer a no-code way to build and a more structured, flow-based way, so the old framing of “developer platform against no-code builder” no longer describes them well. The more useful test is who will keep the agent working in six months, and what kind of contract suits your call volume. CentriWeb builds and looks after voice agents for clients, on platforms of this kind, so weigh our view with that in mind. Facts below are from each vendor’s own pages as at November 2026; check their pages for current prices.
Retell AI vs Synthflow in one table
| Question | Retell AI | Synthflow |
|---|---|---|
| What it is | A platform to build, test, deploy and monitor voice and chat agents | An enterprise conversational AI platform that works inside your phone system |
| How you buy it | Pay as you go per minute, no minimums or contracts | Annual enterprise agreement, quoted by sales |
| Ways to build | Single prompt, or a node-based conversation flow; API and SDKs | Prompt Builder (no-code), Flow Designer (low-code), Platform API (pro-code) |
| Who maintains it | You or whoever you hire | You or whoever you hire, with launch support scoped in the contract |
| Who it suits | Businesses that want to start small and pay for what they use | Contact centres, outsourced call teams and multi-location brands |
How each one charges
Retell AI
Retell’s pricing page lists voice agents at $0.07 to $0.31 a minute on pay as you go, made up of a $0.055 voice engine fee plus the voice, language model and telephony you choose. New accounts get $10 in free credits, 20 concurrent calls are included, and the page says there are no minimums or contracts. Calls are billed to the second. Our guide to Retell AI pricing works through a month’s bill.
Synthflow
Synthflow’s pricing page lists one plan, Enterprise, sold as an annual agreement. It says pricing is scoped to your call volume, phone system, integrations, security needs and launch support, and it publishes no monthly price or per-minute rate. You contact sales for a quote.
If you’ve read older comparisons that quote Synthflow’s monthly plans, those plans are not on its pricing page now. Ask for a written quote that shows what happens if your volume is lower or higher than forecast, and what the renewal terms are.
How each one is built
Both platforms give you two ways to define an agent, and the choice matters more than the brand.
- One prompt. You describe the agent in plain language. Retell calls this a single prompt agent. Synthflow’s documentation calls it Prompt Builder and describes it as its no-code option for non-technical users. This copes better with callers who go off script, because the model can improvise.
- A flow of steps. You lay the call out as nodes: greet, ask, branch, book, end. Retell’s documentation calls this a conversation flow, for calls that must follow a fixed sequence. Synthflow calls it Flow Designer and classes it as low-code, suited to structured and compliance-heavy calls.
Synthflow’s guidance on choosing is a useful rule on either platform: if your single prompt is filling up with conditions, or covers more than three or four stages of a call, move to a flow. It also notes that flow agents need every edge case handled explicitly, which gives more control and more to maintain.
For developers, Retell offers an API, SDKs and an MCP server, and Synthflow offers a Platform API aimed at scripted and multi-tenant setups. Synthflow’s docs also describe white-label subaccounts and billing them through Stripe, which is aimed at businesses reselling agents.
Getting an Australian number onto either platform
Retell’s number guide says it sells US and Canada numbers only, and that numbers from other countries come through your own telephony provider or an imported number. Synthflow’s documentation says you can buy or import a number and attach it to an agent, and its homepage describes agents working inside your existing phone system.
For an Australian or New Zealand business, that means planning how your current number will forward to the agent, and what happens to the call when the agent hands over to a person. Test the handover from a mobile and a landline before you go live, and check that the caller ID your team sees still makes sense.
Where each one is strong
Retell AI
- You can start with free credit and a single agent, and spend grows with minutes.
- A no-code studio that the Retell homepage says a customer service team can build in, with developers extending it.
- Built-in CRM sync for Salesforce, HubSpot, Dynamics 365, GoHighLevel and Zoho, plus simulation and A/B testing.
- Published compliance claims including HIPAA, GDPR and SOC 2, which a clinic should check against its own obligations.
Synthflow
- A contract scoped to your phone system, integrations and launch, which suits a business that wants the vendor involved in the setup.
- The Synthflow homepage names Salesforce, HubSpot, Zendesk and Freshworks, plus phone systems such as Zoom and Five9, and cites more than 200 integrations.
- Three build modes, from plain language to API, so different people on a larger team can each work at their level.
- A clear focus on contact centres and multi-location brands, with concurrency, routing and fallback planned as part of the contract.
Who can keep it working in six months
No-code makes the first version faster. It doesn’t remove the monthly work: reading transcripts, adjusting the prompt when prices or hours change, fixing a booking rule that confused callers, and checking that calendar and CRM connections still work after an update.
Ask three questions before you sign up to either.
- Who on your team will read calls every week? If the answer is nobody, the agent will drift as your business changes.
- Can that person work in the builder? A prompt agent suits an office manager. A flow agent with custom actions suits someone who thinks in steps and data. API work needs a developer.
- What happens when the integration breaks? On pay as you go, you or your contractor fix it. On an enterprise agreement, check in writing what support covers after launch.
A small clinic answering a few dozen calls a day is unlikely to want an annual contract scoped for a contact centre. A group of clinics with a central booking line might. Our page on systems for health and fitness businesses covers where a phone agent sits alongside booking software.
When a built and looked after system fits better
A self-serve platform suits a business with modest call volume, an owner or staff member who enjoys this kind of work, or needs the standard setup already covers. In those cases, start on pay as you go and keep it simple. If neither fits, see Retell AI alternatives and how to choose between them.
A system built and looked after for you suits a business where every missed or mishandled call costs money, where the agent must book into the real calendar and write to the CRM, and where nobody wants to own the prompt and the integrations month after month. That is the work our AI receptionist and voice agent service covers. If Synthflow’s move to annual contracts has you looking around, our guide to Synthflow alternatives groups the other options by type.
A quick way to decide
- Low to moderate volume, want to try it first: Retell’s pay as you go, or another self-serve platform.
- High volume, several sites, existing contact centre phone system: talk to Synthflow and compare its quote with a self-serve platform at your volume.
- No one to maintain it: decide who will look after it before choosing either.