Vapi vs Synthflow: Self-Serve Developer API or Sales-Led Platform

Vapi and Synthflow are both hosted, closed-source voice agent platforms, sold in opposite ways. Vapi is self-serve: $0.05 a minute for hosting, with models at provider cost. Synthflow sells one plan, Enterprise, with contracts from $30,000 a year. For code you can run yourself, there is Dograh, an open-source, self-hostable voice agent platform.

Key Takeaways

• Vapi starts self-serve at $0.05 a minute; Synthflow contracts start at $30,000 a year.
• Synthflow keeps a visual Flow Designer; Vapi's visual Workflows stopped in August 2026.
• For on-prem without an Enterprise contract, self-host Dograh, which is open source.

This post is part of our guide to Synthflow alternatives. The guide's section "Hosted alternatives to Synthflow" sums Vapi up in one line: "Vapi is a self-serve developer platform, where Synthflow is a sales-led one." Here are the two side by side, on every point that changes a buying decision. The last section covers Dograh, an open-source, self-hostable voice agent platform.

A developer API against a sales-led platform

Vapi sells minutes you can buy today, while Synthflow sells a contract you scope with its sales team. Most of the rows below follow from that.

The Vapi figures come from Vapi's pricing page and its package docs. Vapi's packages are sold only to new customers, and accounts on older pricing keep their own terms.

What each one costs to start

Vapi's bill grows with your minutes and the models you choose, while Synthflow's starts at a fixed annual floor. On Vapi, 10,000 minutes a month means $500 of hosting, plus the speech-to-text, language model and voice you pick at each provider's price. Past 4 calls at once you need a package or extra lines: Core costs $29 a month for 10, and each extra line is $10 a month. Phone transport is free on Vapi's own telephony and SIP, and your own carrier bills at its own rates. Our breakdown of Vapi pricing prices every line.

On Synthflow, the pricing page says "Enterprise contracts start at $30,000 annually," with the final price "scoped around call volume, concurrency, telephony setup, integrations, security needs, and launch support." Usage is counted per second, with partial seconds rounded up, and your exact rates come from your agreement. The contract also buys work Vapi leaves to you: implementation, testing, training and launch support.

So the two only compare at real volume. A small pilot costs a few dollars on Vapi, while on Synthflow it starts with a sales conversation. Our post on Synthflow pricing explains what the contract covers and how the floor works out each month.

Model choice on each platform

On Vapi the model is yours to pick, while on Synthflow your plan decides the list. Vapi treats each layer of the call as a part you can swap. Its FAQ says "You can bring your own custom models for any part of the pipeline," through your own provider keys or a custom LLM at a URL you host. That makes it easy to try a cheaper or newer model, and it makes you responsible for testing each combination.

Synthflow's AI Model selector lists OpenAI models from GPT-4o to GPT-6-Luna, plus Synthflow LLM and Advanced Synthflow LLM. Synthflow's model settings say "GPT and other third-party models are only available on Enterprise plans," and "Synthflow LLM is the only model available to non-enterprise customers." Every plan on sale is Enterprise, so that last line applies to workspaces still on the older Pro, Growth and Agency plans. Your own OpenAI key appears only when BYOK access is enabled for your account, and Azure OpenAI connects with your own endpoint and key.

Building an agent: Squads or the Flow Designer

Synthflow still lets you draw a call as nodes on a canvas, and Vapi no longer does. Vapi builds with Assistants, single agents set up in the dashboard or by API, and Squads, groups of assistants that hand a call between them. Vapi's Workflows notice says Workflows were retired on 18 August 2026 and stopped running the next day, with Squads as the recommended replacement. Composer, in the dashboard, can draft a Squad from a plain-language request, and Vapi says to review and test that draft before going live.

On Synthflow, each agent uses either Prompt Builder, where one prompt defines the agent, or the Flow Designer, with nodes for conversation steps, branches, call transfer, real-time booking and more. A Trigger Subflow node hands the call to a sub-agent and returns to the main flow when it finishes. Workflows handle the business steps around a call, such as syncing data to a CRM, and sit on the Enterprise plan. Every publish saves a new version, and each version can be exported to JSON, without its actions or knowledge bases.

A team without developers usually reaches a first working agent faster on a drawn flow. A developer team that wants every part under its own code will find Vapi's API closer to how it works.

Open Source Alternative to Vapi / Retell

Self-hosted voice agent platform — no per-minute fees

dograh-hq/dograh

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HIPAA, hosting and data controls

Vapi sells HIPAA as a monthly add-on on any package, while Synthflow writes its BAA into the Enterprise contract. Vapi's HIPAA add-on costs $2,000 a month. Vapi emails the BAA for signature from the dashboard, and HIPAA mode can't run together with zero data retention. Synthflow signs its BAA at contract signing for customers using the HIPAA Setting, which is off by default. Generally, whichever vendor signs, a BAA hands it obligations while your own HIPAA duties stay with you; confirm your position with counsel.

On hosting, Vapi runs on Vapi's cloud. Synthflow runs on its own cloud, with region-based hosting in the US and EU. Its EU cluster keeps all data and processing in the European Union, and it is retiring its older Global cluster during Q4 2026, moving those workspaces to a US or EU cluster.

Data controls differ too. Vapi keeps raw call data for 14, 30 or 180 days depending on the package. Synthflow has an agent toggle that deletes transcripts, recordings and caller IDs after 30 days, and PII redaction for transcripts, webhooks and logs on new calls. For certificates, Vapi lists SOC 2 Type II, HIPAA and GDPR, and Synthflow's trust center adds ISO/IEC 27001 and PCI DSS v4.0.1.

Picking between them

Pick Vapi if your developers want to choose every model and start on a few dollars of credit. Pick Synthflow if you want the vendor to build and launch the agent under one contract, with a drawn flow and EU processing.

Teams that liked Vapi's Workflows now face a rebuild on Squads anyway, which makes it a natural point to compare a drawn-flow platform. Teams weighing a third hosted option can read Retell AI vs Synthflow and Bland AI vs Synthflow.

Run the same call script on both over a real phone line before you sign. Most phone calls still reach the agent as 8 kHz audio, while a browser demo runs at 16 kHz, so a demo that sounds sharp can mishear callers on the phone.

Where an open-source platform fits

Both are hosted and closed source: Vapi runs on its own cloud, and Synthflow on its own cloud in the US or EU. Neither gives you code you can run without a vendor contract, and that is where Dograh fits.

Dograh is open source under BSD-2-Clause, and its GitHub repository, with more than 5,900 stars, holds the whole platform. Its visual workflow builder joins nodes with pathways, each with a written condition the AI reads to pick its route, so a team used to the Flow Designer will find it familiar. A sub-flow that returns is drawn as one pathway in and one back, so you add the return yourself.

Dograh is the orchestration layer: it runs the call flow, tools and telephony, and the speech and language models are a separate layer you choose. As on Vapi, that can be Dograh's own models, a provider on your own key, or open-weight models you host. The call audio stays in-house only when the speech and language models run on your own servers too. Your numbers stay with your carrier, such as Twilio, Vonage, Plivo or Telnyx. Transfer Call works on Twilio, Telnyx and Asterisk ARI. It passes no summary by default; on Twilio it can play a short spoken introduction to both people. Write the details to your system with an HTTP API tool before the transfer.

Self-hosted Dograh has no per-minute platform fee (servers, model keys and phone minutes still cost); Dograh Cloud has a 1¢-a-minute platform fee. Cloud includes 10 concurrent calls. Self-hosting puts uptime in your team's hands, and since there is no one-click import from Vapi or Synthflow, each agent is rebuilt.

Dograh is the strongest fit when you want Vapi's model choice and a drawn flow like Synthflow's without a vendor contract, because the code is yours to run. To try it, self-host it with Docker Compose, or start on Dograh Cloud.