Top 6 of 18 researched candidates
Alternatives to Synthflow
Find a better fit for what you need. Compare alternatives to Synthflow with sourced features, strengths and trade-offs side by side.
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Evidence-backed shortlist
Closest researched alternatives to Synthflow
Ordered by the requirements met, strengths preserved, explicit trade-offs and research coverage. Sponsorship does not enter the order.
- 01
ElevenLabs Agents
Hosted platform for building voice and chat agents, with telephony, SDKs and a choice of LLM.
From FreeWhy it's on this listClaude · YesAnthropic models are natively selectable in agent settings; a few older Claude models drop out in EU data-residency workspaces.Evidence ↗
Where it improves on Synthflow
- +Open models · YesOpen-weight models run two ways: ElevenLabs-hosted Qwen in the native model list, or Llama and Mixtral through a custom LLM endpoint such as Together AI, Groq or SambaNova.Evidence ↗
- +Model choice · YesYou pick the model per agent, plus a backup cascade; LLM usage is billed on top of the plan and varies by model.Evidence ↗
Trade-offs against Synthflow
- −In your editor · NoThe vendor enumerates its surfaces as web widgets, mobile apps, phone systems and custom integrations; no editor or IDE extension appears in that list.Evidence ↗
- −Admin controls · PartialGuardrails constrain what an agent may say and per-tool approval constrains what it may do, but Guardrails is in Alpha and enabling MCP servers is not restricted to admins.Evidence ↗
- −Data residency · PartialUS by default; EU, India and Singapore exist as separate Enterprise workspaces with their own accounts, API hosts and reduced model choice, and processing may still leave the region.Evidence ↗
35/35 researched criteria - 02
AudioCodes Live Hub
Self-service cloud platform for building voice AI agents and connecting them to real telephony channels.
From $0.05/minuteWhy it's on this listClaude · PartialClaude models are supported only as bring-your-own custom models configured with your own Anthropic API key; the pre-deployed model list carries OpenAI and Google models only.Evidence ↗
Where it improves on Synthflow
- +Open models · PartialOpen-weight models such as gpt-oss and Gemma are reachable only through the bring-your-own-model path with your own Groq, Cerebras or OpenAI keys, not from the pre-deployed set.Evidence ↗
- +Model choice · YesYou choose the LLM per agent from pre-deployed models or add your own provider, and you can equally bring an entirely external conversational AI platform instead.Evidence ↗
Trade-offs against Synthflow
- −Agent permissions · PartialAn agent calls any tool you configured without a per-call approval step, so control is exercised up front by choosing its tools; the MCP management connection does offer an explicit read-only mode.Evidence ↗
- −In your editor · NoThere is no editor or IDE extension: authoring happens in the web portal, and the only documented developer-tool integrations are the two MCP clients named below.Evidence ↗
- −Free tier · PartialYou can sign up and test without a credit card on $10 of complimentary credit, but that is a limited Trial plan that goes inactive at a zero balance rather than a standing free tier.Evidence ↗
33/35 researched criteria · 2 not established - 03
Vapi
Developer platform for building, testing and deploying voice AI agents that make and receive phone calls.
From $0.05/minuteWhy it's on this listClaude · YesClaude is selectable as the assistant's LLM, on Vapi's integration or your own Anthropic account.Evidence ↗
Where it improves on Synthflow
- +Open models · YesOpen-weight models reach the pipeline through Groq, Together AI, Mistral, DeepSeek and OpenRouter, or a self-hosted server.Evidence ↗
- +Model choice · YesYou choose transcriber, LLM and voice independently and can swap any of them.Evidence ↗
Trade-offs against Synthflow
- −Agent permissions · PartialTools fire mid-call without human approval; a per-tool rejection plan is the mechanism that withholds an action.Evidence ↗
- −Opt out of training · PartialThe privacy policy reserves call content for model training and names no toggle; the $1,000/month ZDR add-on is the only documented way to stop it being kept at all.Evidence ↗
- −Data residency · PartialUS is the default region; the EU region is frozen to existing accounts and new EU residency is enterprise-only, so regional control comes from your own buckets and models.Evidence ↗
35/35 researched criteria - 04
PolyAI
Enterprise platform for building voice and chat agents that resolve customer calls, priced per minute.
Why it's on this listClaude · YesClaude is one of the third-party models you can run instead of Raven; the model docs list Claude options under the Amazon Bedrock provider tab, selectable per channel.Evidence ↗
Where it improves on Synthflow
- +Open models · PartialThe model catalogue enumerates only Raven, OpenAI and Amazon Bedrock (Claude, Nova) with no open-weight option, but you can attach your own LLM endpoint.Evidence ↗
- +Model choice · YesYou choose the model per channel in voice and chat configuration; Raven is the recommended default rather than the only option.Evidence ↗
Trade-offs against Synthflow
- −Multi-agent · NoThe only 'team of agents' feature is assigning several TTS voices to one agent; no coordination between multiple agents on a single task is documented, and the build assistant works one branch at a time.Evidence ↗
- −Agent permissions · PartialWren plans and waits for approval by default, always asks before writing to the live environment, never receives secret values, and its API discovery requests are GET-only.Evidence ↗
- −Pooled budget · PartialConversation volume draws on one account-level Subscription Volume of CX Tokens, but the Wren builder allowance is per person and not shared.Evidence ↗
35/35 researched criteria - 05
Retell AI
Pay-as-you-go platform for building, testing and running AI phone, chat and SMS agents.
From $0.07/minuteWhy it's on this listClaude · YesClaude models are selectable as the agent's conversation model and priced per minute for voice and per message for chat, alongside GPT and Gemini options.Evidence ↗
Where it improves on Synthflow
- +Open models · PartialRetell's own model menu is limited to hosted GPT, Claude and Gemini, but the custom-LLM path lets you put a self-hosted open-weights model behind the agent over a WebSocket you operate.Evidence ↗
- +Model choice · YesYou pick the conversation model per agent from a published, per-minute-priced list, and you can substitute your own model entirely through the custom-LLM WebSocket.Evidence ↗
Trade-offs against Synthflow
- −Agent permissions · PartialProhibited-topic guardrails screen both the agent's replies and user input, and tools are explicitly wired per node, but guardrails only swap in a placeholder message rather than stopping or escalating the call.Evidence ↗
- −Free tier · PartialYou can sign up and run real calls without talking to sales, but the free allowance is a one-off $10 trial credit per email address rather than a standing free plan.Evidence ↗
- −Admin controls · PartialAdmin, Developer and Member roles constrain who can edit agents, see raw transcripts or change limits, but the pricing comparison marks role-based access control as an Enterprise capability rather than a pay-as-you-go one.Evidence ↗
34/35 researched criteria · 1 not established - 06
Cartesia
Real-time speech models and a managed runtime for production phone and web voice agents.
From FreeWhy it's on this listClaude · YesAnthropic Claude models are named in the SDK's supported-models table and used in its examples.Evidence ↗
Where it improves on Synthflow
- +Open models · PartialThe LLM layer routes through LiteLLM to 100+ providers, but the vendor names only Anthropic, OpenAI and Google, and its own speech models are API-only.Evidence ↗
- +Model choice · YesYou pick the agent's LLM and can swap it in the Playground or API; Cartesia owns the speech models and manages the LLM integration.Evidence ↗
Trade-offs against Synthflow
- −Done-for-you service · NoSelf-serve software: you build and deploy the agent yourself; sales contact exists for Enterprise terms, not for building it for you.Evidence ↗
- −Multi-agent · NoSystem tools enumerate three slots: end call, DTMF, and transfer to an E.164 phone number. An agent therefore hands off to a number, not to another Cartesia agent.Evidence ↗
- −Agent permissions · PartialLimits are prompt-level guardrails plus per-tool execution settings (timeout, immediate vs async, speak-before-acting); there is no separate policy engine.Evidence ↗
35/35 researched criteria
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How the shortlist is calculated
Comparable first. We consider listings in the same category as Synthflow and alternatives previously researched for this page.
Requirements first. We prioritise your selected needs, then shared strengths, fewer documented trade-offs, more complete research and finally alphabetical order.
Unknown remains unknown. Missing evidence is never converted into a benefit or a trade-off. Every improvement shown above comes from the same sourced criterion as the listing.
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