Vapi
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.
At a glance
- Type
- Developer platform for AI voice agents (programmable telephony)
- Tier
- T1
- Section
- Voice agent platforms
- Created
- 2023 (YC W23)
- Latest release
- not applicable — not OSS
- License
- not applicable — not OSS
- Pricing
- Per-minute usage ($0.05/min base + provider passthrough)
- Funding
- $20M Series A Dec-2024 (Bessemer); $130M val
Taxonomy
- storage
- kv
- retrieval
- injection
- persistence
- session
- update
- agent-controlled
- unit
- turn
- governance
- opaque
- conflict
- stateless
When to use
Optimised for: Building phone-call voice agents quickly with composable STT/LLM/TTS
Anti-fit: Telephony-centric — not for in-app voice UX; per-minute pricing scales fast at high volume
Pros & cons
Pros
Category-leading mindshare; Bessemer-backed; SOC 2 + HIPAA; mature webhooks + SDKs.
Cons
Per-minute economics at scale; provider-passthrough means triple vendor exposure (STT + LLM + TTS).
Claims & capabilities
$20M Series A Dec-2024 (Bessemer lead); >$10M ARR reported Q1 2025; YC W23
Technical surface
- API surface
- REST API; SDKs (Python, JS, React); webhooks
- Backend storage
- Call state in Vapi-managed DB; transcripts retained per config
- Deployment
- Cloud-managed; private deployments on Enterprise tier
- Embedding model
- not applicable — not a memory product
- Multi-tenancy
- Multi-tenant cloud; Enterprise dedicated tier
- MCP
- Tool-calling supports MCP servers (caller-side)
- A2A
- searched not found
- OpenTelemetry
- searched not found
Compare Vapi with…
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.
- 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.
- LiveKit Agents T1
LiveKit Agents — agent framework built on LiveKit's open-source WebRTC media server. LiveKit raised $45M Series B Sep-2024 ($300M val). Powers OpenAI Realtime API's WebRTC transport (LiveKit is the substrate OpenAI chose). Agents framework formally launched 2024.
Related systems
References (2)
- Anthropic Claude (foundation models) depends on at runtime — adjacent-infrastructure cell: Twilio / Vonage SIP; Deepgram + Cartesia + Eleven STT/TTS; Anthropic / OpenAI LLMs
- OpenAI GPT family (GPT-5 / GPT-4o / o3 / o4) depends on at runtime — adjacent-infrastructure cell: Twilio / Vonage SIP; Deepgram + Cartesia + Eleven STT/TTS; Anthropic / OpenAI LLMs
Referenced by (1)
- Retell AI competes with — er founders. Direct competitor to Vapi with proprietary-model focus.