Top 6 of 15 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
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 - 03
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 - 04
Retell AI
Platform for building, testing and deploying AI voice and chat agents on phone, web and SMS, billed per minute.
From $0.07/minuteWhy it's on this listClaude · YesClaude Sonnet and Haiku models are selectable for voice agents, priced per minute, and for chat agents per AI message.Evidence ↗
Where it improves on Synthflow
- +Open models · PartialThe hosted model menu enumerates only OpenAI, Anthropic and Google models, so no open-weight model is offered, but the custom LLM WebSocket path exists precisely so you can host one yourself.Evidence ↗
- +Model choice · YesYou pick the LLM per agent from a published menu of 20+ models, each with its own per-minute rate, plus a fast tier and a custom-LLM escape hatch.Evidence ↗
Trade-offs against Synthflow
- −Agent permissions · PartialThe agent completes calls without asking, but a human can monitor live and seize the call, and guardrails plus PII removal are configurable metered add-ons.Evidence ↗
- −Admin controls · PartialRole-based access control is sold as an Enterprise line, marked absent for pay-as-you-go in the plan table, yet the docs describe Admin/Developer/Member roles with no tier restriction; API keys can be scoped read or edit on any plan. Contradiction recorded in notes.Evidence ↗
- −Opt out of training · NoThe privacy policy lists training its AI models among the uses of collected data, and its 'Your Choices' section offers only account deletion, cookie preferences, marketing opt-out and sale/sharing opt-out, with no training opt-out.Evidence ↗
34/35 researched criteria · 1 not established - 05
AudioCodes Live Hub
Self-service SaaS for building voice AI agents and connecting them to SIP trunks, Teams, WhatsApp and WebRTC.
From $0.05/minuteWhy it's on this listClaude · PartialAnthropic is reachable only as a bring-your-own-key custom model; the pre-deployed catalogue Live Hub bills for is OpenAI and Google only.Evidence ↗
Where it improves on Synthflow
- +Open models · PartialOpen-weight models run only as custom models on your own Groq, Cerebras or OpenAI keys; none appear in the pre-deployed list Live Hub hosts.Evidence ↗
- +Model choice · YesYou choose the LLM per agent and may substitute any supported provider with your own key, and equally bring a third-party conversational AI platform instead.Evidence ↗
Trade-offs against Synthflow
- −Agent permissions · PartialLimits are set at design time: tool allow-lists, valid transfer numbers, Max turns. The vendor warns prompt guardrails are not a security boundary, and there is no runtime human approval step.Evidence ↗
- −In your editor · NoNo editor plug-in exists; the two supported external clients are Claude Code and Claude Desktop over MCP, and neither is an IDE.Evidence ↗
- −Admin controls · PartialRBAC is real but fixed: admins assign users and API clients to predefined groups and cannot create a group or edit a policy of their own.Evidence ↗
33/35 researched criteria · 2 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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