# Alternatives to Synthflow > Source: https://theagentsindex.com/synthflow-ai/alternatives (current datasheets, evidence-ranked) Candidates share the baseline category or are previously researched peers. Requirements, preserved strengths, explicit trade-offs and research coverage decide the order; paid tier does not. ## Shortlist ### 1. ElevenLabs Agents Hosted platform for building voice and chat agents, with telephony, SDKs and a choice of LLM. **Research coverage:** 35/35 criteria **Where it improves on Synthflow:** - [Claude: yes — Anthropic models are natively selectable in agent settings; a few older Claude models drop out in EU data-residency workspaces.](https://elevenlabs.io/docs/eleven-agents/customization/llm) - [Open models: yes — Open-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.](https://elevenlabs.io/docs/eleven-agents/customization/llm/custom-llm/together-ai) - [Model choice: yes — You pick the model per agent, plus a backup cascade; LLM usage is billed on top of the plan and varies by model.](https://elevenlabs.io/docs/eleven-agents/customization/llm) **Trade-offs against Synthflow:** - [In your editor: no — The vendor enumerates its surfaces as web widgets, mobile apps, phone systems and custom integrations; no editor or IDE extension appears in that list.](https://elevenlabs.io/docs/eleven-agents/integrate/overview) - [Admin controls: partial — Guardrails 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.](https://elevenlabs.io/docs/eleven-agents/best-practices/guardrails) - [Data residency: partial — US 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.](https://elevenlabs.io/docs/overview/administration/data-residency) [View ElevenLabs Agents](https://theagentsindex.com/elevenlabs-conversational-ai) ### 2. Vapi Developer platform for building, testing and deploying voice AI agents that make and receive phone calls. **Research coverage:** 35/35 criteria **Where it improves on Synthflow:** - [Claude: yes — Claude is selectable as the assistant's LLM, on Vapi's integration or your own Anthropic account.](https://docs.vapi.ai/providers/model/anthropic) - [Open models: yes — Open-weight models reach the pipeline through Groq, Together AI, Mistral, DeepSeek and OpenRouter, or a self-hosted server.](https://vapi.ai/platform) - [Model choice: yes — You choose transcriber, LLM and voice independently and can swap any of them.](https://vapi.ai/platform) **Trade-offs against Synthflow:** - [Agent permissions: partial — Tools fire mid-call without human approval; a per-tool rejection plan is the mechanism that withholds an action.](https://docs.vapi.ai/tools/tool-rejection-plan) - [Opt out of training: partial — The 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.](https://vapi.ai/privacy) - [Data residency: partial — US 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.](https://docs.vapi.ai/security-and-privacy/data-flow) [View Vapi](https://theagentsindex.com/vapi) ### 3. PolyAI Enterprise platform for building voice and chat agents that resolve customer calls, priced per minute. **Research coverage:** 35/35 criteria **Where it improves on Synthflow:** - [Claude: yes — Claude 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.](https://poly.ai/blog/agentic-dialog-platform-open-to-builders) - [Open models: partial — The model catalogue enumerates only Raven, OpenAI and Amazon Bedrock (Claude, Nova) with no open-weight option, but you can attach your own LLM endpoint.](https://docs.poly.ai/behavior/models/byom) - [Model choice: yes — You choose the model per channel in voice and chat configuration; Raven is the recommended default rather than the only option.](https://docs.poly.ai/behavior/models/model-use) **Trade-offs against Synthflow:** - [Multi-agent: no — The 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.](https://docs.poly.ai/voice-channel/multi-voice) - [Agent permissions: partial — Wren 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.](https://docs.poly.ai/wren/building) - [Pooled budget: partial — Conversation volume draws on one account-level Subscription Volume of CX Tokens, but the Wren builder allowance is per person and not shared.](https://docs.poly.ai/wren/usage-and-limits) [View PolyAI](https://theagentsindex.com/polyai) ### 4. Retell AI Platform for building, testing and deploying AI voice and chat agents on phone, web and SMS, billed per minute. **Research coverage:** 34/35 criteria **Where it improves on Synthflow:** - [Claude: yes — Claude Sonnet and Haiku models are selectable for voice agents, priced per minute, and for chat agents per AI message.](https://www.retellai.com/pricing) - [Open models: partial — The 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.](https://docs.retellai.com/integrate-llm/overview) - [Model choice: yes — You 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.](https://docs.retellai.com/build/single-multi-prompt/configure-basic-settings) **Trade-offs against Synthflow:** - [Agent permissions: partial — The 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.](https://www.retellai.com/) - [Admin controls: partial — Role-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.](https://www.retellai.com/pricing) - [Opt out of training: no — The 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.](https://www.retellai.com/legal/privacy-policy) [View Retell AI](https://theagentsindex.com/retell-ai) ### 5. AudioCodes Live Hub Self-service SaaS for building voice AI agents and connecting them to SIP trunks, Teams, WhatsApp and WebRTC. **Research coverage:** 33/35 criteria **Where it improves on Synthflow:** - [Claude: partial — Anthropic is reachable only as a bring-your-own-key custom model; the pre-deployed catalogue Live Hub bills for is OpenAI and Google only.](https://techdocs.audiocodes.com/livehub/Content/AI-Agents/Bring%20your%20own%20models.htm) - [Open models: partial — Open-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.](https://techdocs.audiocodes.com/livehub/Content/AI-Agents/Bring%20your%20own%20models.htm) - [Model choice: yes — You 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.](https://techdocs.audiocodes.com/livehub/Content/AI-Agents/Bring%20your%20own%20models.htm) **Trade-offs against Synthflow:** - [Agent permissions: partial — Limits 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.](https://techdocs.audiocodes.com/livehub/Content/AI-Agents/Prompt%20engineering.htm) - [In your editor: no — No editor plug-in exists; the two supported external clients are Claude Code and Claude Desktop over MCP, and neither is an IDE.](https://techdocs.audiocodes.com/livehub/Content/AI-Agents/MCP%20server.htm) - [Admin controls: partial — RBAC 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.](https://techdocs.audiocodes.com/livehub/Content/VAIC/User-Groups.htm) [View AudioCodes Live Hub](https://theagentsindex.com/audiocodes-live-hub) ### 6. Cartesia Real-time speech models and a managed runtime for production phone and web voice agents. **Research coverage:** 35/35 criteria **Where it improves on Synthflow:** - [Claude: yes — Anthropic Claude models are named in the SDK's supported-models table and used in its examples.](https://docs.cartesia.ai/line/sdk/agents) - [Open models: partial — The 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.](https://docs.cartesia.ai/line/sdk/agents) - [Model choice: yes — You pick the agent's LLM and can swap it in the Playground or API; Cartesia owns the speech models and manages the LLM integration.](https://docs.cartesia.ai/agents/models) **Trade-offs against Synthflow:** - [Done-for-you service: no — Self-serve software: you build and deploy the agent yourself; sales contact exists for Enterprise terms, not for building it for you.](https://www.cartesia.ai/agents) - [Multi-agent: no — System 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.](https://docs.cartesia.ai/agents/system-tools) - [Agent permissions: partial — Limits are prompt-level guardrails plus per-tool execution settings (timeout, immediate vs async, speak-before-acting); there is no separate policy engine.](https://docs.cartesia.ai/agents/configuration) [View Cartesia](https://theagentsindex.com/cartesia) ## Method Unknown data is never treated as a benefit or a trade-off. Featured placement is labelled but cannot alter recommendation order.