Voice agent platforms
13 systems in the voice agent platforms category of the AI Agent Infrastructure Landscape, grouped by maturity tier.
Tier 1 — battle-tested (9)
- Bland AI Developer platform for AI phone agents (vertically integrated)
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.
- Cartesia Sonic Real-time TTS + voice-agent platform (Cartesia)
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 Son…
- ElevenLabs Conversational AI Voice-agent platform from a TTS-first vendor (ElevenLabs)
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-…
- Hume EVI Empathic voice-AI platform (voice + emotion)
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…
- LiveKit Agents Voice-agent framework on LiveKit WebRTC platform
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 framewo…
- OpenAI Realtime API Speech-to-speech LLM API (OpenAI Realtime)
OpenAI's Realtime API for native speech-to-speech multimodal interaction with GPT-4o — launched Oct 2024 (DevDay). Skips the STT → LLM → TTS pipeline by passing speech directly to GPT-4o. The platform substrate that Vapi/Retell/Bland int…
- Pipecat (Daily) OSS voice-agent framework (Daily.co)
Open-source Python framework for real-time voice + multimodal AI agents, maintained by Daily.co. Pipeline-style architecture (STT → context → LLM → TTS) wired over WebRTC. The OSS substrate that many of the voice platforms build on or co…
- Retell AI Developer platform for AI voice agents (low-latency)
Voice-agent platform with vendor focus on sub-800ms turn latency and proprietary voice models. Y Combinator S24; raised $4.6M seed Aug 2024 (BoxGroup + others); >$1M ARR by month 6 per founders. Direct competitor to Vapi with proprietary…
- Vapi Developer platform for AI voice agents (programmable telephony)
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 r…
Tier 2 — production-ready (4)
- CallRail Conversation Intelligence Conversation intelligence / call analytics platform
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 runt…
- Speechmatics Flow Conversational voice-agent platform (Speechmatics)
Speechmatics (UK; STT leader) launched Flow Q4 2024 — conversational voice-agent platform composed on Speechmatics STT + caller LLM. Speechmatics raised $62M Series B (2022); enterprise + media customers. UK / EU data-residency lead.
- Synthflow No-code voice-agent builder (telephony)
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.
- Vonage AI Studio Enterprise CPaaS voice-agent builder (Vonage / Ericsson)
Vonage's AI Studio — visual conversational-agent designer that runs on Vonage CPaaS (SMS / Voice / WhatsApp). Vonage acquired by Ericsson 2022 ($6.2B); AI Studio is the conversational AI layer of the broader CPaaS. Enterprise focus.