Synthflow
No-code voice-AI platform — drag-and-drop call-flow builder targeted at non-developers. Berlin-based; raised $7.4M Series A Sep-2024 (Singular). Distinguishes itself from Vapi/Retell with visual call-flow builder rather than code-first SDK.
At a glance
- Type
- No-code voice-agent builder (telephony)
- Tier
- T2
- Section
- Voice agent platforms
- Created
- 2023 (founded)
- Latest release
- not applicable — not OSS
- License
- not applicable — not OSS
- GitHub
- not applicable — no GitHub repo
- Pricing
- Tiered: Starter $29/mo + per-minute; Pro $450/mo
- Funding
- $7.4M Series A Sep-2024 (Singular lead)
Taxonomy
- storage
- kv
- retrieval
- injection
- persistence
- session
- update
- agent-controlled
- unit
- turn
- governance
- opaque
- conflict
- stateless
When to use
Optimised for: SMB voice agents via visual builder; EU residency
Anti-fit: No-code-first → less flexible than Vapi/Retell for complex programmatic use cases
Pros & cons
Pros
No-code builder; EU data residency; SOC 2 + GDPR; SMB-friendly pricing.
Cons
Smaller / EU-centric; less programmatic than Vapi; vendor-pipeline (not vertically integrated).
Claims & capabilities
$7.4M Series A Sep-2024 (Singular); no-code visual builder; EU residency option
Technical surface
- API surface
- REST API + dashboard + Zapier integration
- Backend storage
- Call state in Synthflow-managed DB
- Deployment
- Cloud-managed (EU + US regions)
- Embedding model
- not applicable — not a memory product
- Multi-tenancy
- Multi-tenant cloud
- MCP
- searched not found
- A2A
- searched not found
- OpenTelemetry
- searched not found
Similar systems
Other voice agent platforms in the catalog, ranked by inbound references.
- Cartesia Sonic T1
Cartesia's Sonic TTS — state-space-model-based voice generation, lowest published TTS latency (~40ms). Cartesia raised $64M Series A Q1 2025 (Index + Lightspeed); founded by Mamba authors. Agent platform layer ('Cartesia Line') wraps Sonic with telephony + LLM.
- Vapi T1
Voice-AI developer platform — STT + LLM + TTS pipelines wired to telephony (Twilio / SIP). Used to build outbound + inbound phone agents at scale. Raised $20M Series A from Bessemer + Y Combinator (Dec 2024) at $130M valuation; revenue reported >$10M ARR by Q1 2025.
- Bland AI T1
Voice-AI platform with custom STT + LLM + TTS stack ('the whole pipeline'). Raised $40M Series A Apr-2024 (Lightspeed + Anthology). Distinguished by 'pathway' graphs (deterministic call flows) and aggressive outbound-calling positioning.
- CallRail Conversation Intelligence T2
CallRail's AI-driven conversation intelligence layer atop their call-tracking product. Marketing-vertical voice analytics — auto-tagging, sentiment, lead scoring. CallRail is profitable / private (Sageview-backed); not a voice-agent runtime but the BI / analytics adjacent layer.
- ElevenLabs Conversational AI T1
ElevenLabs launched Conversational AI Nov-2024 — STT + LLM + their own market-leading TTS in one pipeline. Combines vendor's voice cloning + multilingual TTS strengths with hosted call orchestration. ElevenLabs raised $180M Series C Jan-2025 at $3.3B val.
- Hume EVI T1
Hume's Empathic Voice Interface (EVI) — voice agent platform with vocal-affect understanding. Hume raised $50M Series B Mar-2024 (EQT). Distinguished from pure LLM voice agents by emotion/prosody modelling; uses Hume's proprietary speech-prosody models.
Related systems
References (2)
- Anthropic Claude (foundation models) depends on at runtime — adjacent-infrastructure cell: Twilio; Deepgram; ElevenLabs; OpenAI / Anthropic
- OpenAI GPT family (GPT-5 / GPT-4o / o3 / o4) depends on at runtime — adjacent-infrastructure cell: Twilio; Deepgram; ElevenLabs; OpenAI / Anthropic