Vapi vs Retell vs Bland vs Synthflow (2026): The Voice AI Platform Matrix

Feature matrix

The five platforms across the axes that decide the shortlist. Scroll the table sideways on mobile.

Pricing, line by line

Voice pricing is a platform or voice-engine fee, an LLM cost, and telephony. Some vendors bundle, some pass through. The headline platform fee is the least useful number; the fully-loaded cost depends on the model and the telephony.

Vapi has the lowest platform fee, but it is orchestration only; the real cost is whatever speech and model providers you plug in, and it drops toward $0.05/min when you supply your own keys. Retell spans the widest range because the LLM line runs from $0.003/min (a nano model) to $0.345/min (a realtime model). Bland's lower per-minute rate needs a $299/mo (Build) or $499/mo (Scale) subscription, and telephony is a separate line. Synthflow and ElevenLabs both bill the voice engine and the LLM as distinct lines. The historical Bland "$0.09/min flat" rate is pre-December-2025 and now effectively Enterprise-only.

Latency

A caller reads a pause as a problem. Under ~500ms feels like a conversation, up to ~800ms is acceptable, past ~1000ms feels broken. That budget is split across the pipeline, and the LLM is the biggest and most variable part:

Advertised platform latency (not audited SLAs): Bland ~400ms (product page cites sub-200ms), Retell ~600ms, Vapi ~500 to 800ms. Synthflow and ElevenLabs do not publish a full voice-to-voice figure; ElevenLabs advertises ~75ms for text-to-speech synthesis alone. Because the LLM is 350 to 1000ms of the total, the model you run is the real lever. On Vapi, Retell, or ElevenLabs, a low-time-to-first-token model keeps the whole pipeline under ~800ms; see the voice agent API and latency guide.

Bring your own LLM

The axis that reorganizes the choice. Owning the model means you control cost, latency, fine-tuning, and data residency. Support ranges from a clean base-URL swap to none.

Only Vapi is a paste-a-URL swap. Retell supports a custom model but makes you host a relay. Bland is closed by design, which is the core of its security pitch: one vendor, in-house models, no third-party routing. The cost is you cannot adopt a faster or cheaper model when one ships.

Telephony

All five carry calls over the phone network; they differ in whether numbers are built in and whether you can bring your own carrier.

Compliance

• Vapi — HIPAA is an opt-in add-on. SOC 2 and GDPR are referenced on its security page; confirm your specific certificate with the vendor before relying on it.
• Retell AI — SOC 2 Type 1 and Type 2, HIPAA, and GDPR are documented, with a self-serve BAA and DPA.
• Bland AI — SOC 2 Type II, HIPAA, GDPR, and PCI DSS v4.0 are listed on its site (self-attested); the closed in-house stack is the compliance argument.
• Synthflow — SOC 2, HIPAA, GDPR, and ISO 27001 badges, with EU and US hosting options.
• ElevenLabs Agents — BAAs for HIPAA on the Enterprise tier.

For regulated workloads, confirm a signed BAA on your specific plan with any of these before sending protected health information.

When to pick each

Pick Vapi

• You are a developer who wants the cheapest orchestration fee and to assemble the stack.
• You want a true bring-your-own-LLM base URL and the widest choice of speech providers.

Pick Retell AI

• You are running phone operations at volume and want batch and outbound campaigns.
• You want SOC 2, HIPAA, and GDPR with a self-serve BAA, and SIP to any carrier.

Pick Bland AI

• You are in a regulated industry and want one closed vendor with in-house models.
• You value data that never routes to a third party over the ability to swap the LLM.

Pick Synthflow

• You are a non-engineer or agency and want a working agent from a visual builder.

Pick ElevenLabs Agents

• Voice quality is the deciding factor and you want the best text-to-speech under the agent.

Frequently asked questions

Is Vapi or Retell better?

Vapi is the developer-first orchestration layer at $0.05/min with a true OpenAI-compatible custom LLM. Retell is built for phone operations at volume at $0.07 to $0.31/min, with campaigns, SIP, and SOC 2 plus HIPAA out of the box. Build on Vapi; operate on Retell.

Which is cheapest: Vapi, Retell, Bland, or Synthflow?

Vapi has the lowest platform fee at $0.05/min, but that is orchestration only. Bland is $0.11 to $0.14/min all-in for the AI stack (telephony separate). Retell is $0.07 to $0.31/min. Synthflow starts at $0.09/min plus $0.02 to $0.04/min for the model. Fully loaded, the cheapest depends on the model you run, not the headline fee.

Does Bland AI support a custom LLM?

No. Bland runs a closed in-house stack; its call API accepts only its base and turbo models. There is no custom-LLM parameter and no OpenAI-compatible base URL. Vapi, Retell, and ElevenLabs all support a custom LLM; Synthflow offers a menu of hosted models.

Which voice AI platform has the lowest latency?

By advertised numbers, Bland (~400ms), then Retell (~600ms), then Vapi (~500 to 800ms). None are audited. The LLM's time-to-first-token is 350 to 1000ms of the budget, so a fast model on a bring-your-own-LLM platform is what actually gets you under ~800ms.

What are the best Vapi alternatives?

Retell for production call operations, Bland for a closed single vendor, Synthflow for no-code, and ElevenLabs Agents for voice quality. LiveKit and Pipecat are open-source frameworks for self-hosting the whole pipeline.