Retell AI
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-model focus.
Active · Verified 2026-10-27 · fresh as of 2026-10-27 · 47 cited facts, 5 with a third-party source · 1 recorded change · Suggest a correction
At a glance
- Tier
- T1
- Section
- Voice agent platforms
- Created
- 2024 (YC S24) third-party fix
- Latest release
- not applicable — not OSS fix
- License
- not applicable — not OSS fix
- GitHub
- github.com/RetellAI (SDKs only) repo fix
- Pricing
- Pay-as-you-go $0.07-$0.31/min for voice agents (Retell voice infra $0.055/min plus TTS and LLM components), $10 free credits, 20 concurrent calls included; Enterprise custom vendor fix
- Funding
- $4.6M seed Aug-2024 (BoxGroup + others) third-party fix
- Freshness
- 2026-10-27 fix
- Layer
- agent-infra repo fix
- Licensing
- commercial vendor fix
- SDK languages
- python, rest, typescript vendor fix
- Protocols
- mcp-client, mcp-server vendor fix
- Compliance
- gdpr, hipaa, iso27001, soc2-type2 vendor fix
When to use
Optimised for: Sub-800ms voice turn latency with vertically-integrated stack
Anti-fit: Telephony focus; smaller funding than Vapi; per-minute pricing
Pros & cons
Pros
Latency-first positioning; SOC 2 + HIPAA; YC distribution; clean SDKs.
Cons
Smaller than Vapi; per-minute economics at scale; proprietary stack reduces flexibility.
Claims & capabilities
YC S24; >$1M ARR by month 6; proprietary low-latency voice stack
Technical surface
- API surface
- REST API + Python/JS/Go SDKs; webhooks
- Backend storage
- Call state in Retell-managed DB
- Deployment
- Cloud-managed
- Embedding model
- not applicable — not a memory product
- Multi-tenancy
- Multi-tenant cloud
- MCP
- yes — agents can call MCP tools during live calls
- A2A
- searched not found
- OpenTelemetry
- searched not found
Compare Retell AI with…
Alternatives to Retell AI → live options ranked by shared design, licence, hosting and MCP support
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.
- 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.
- ElevenLabs Conversational AI (now ElevenAgents) 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. As of 2026-10 ElevenLabs markets the platform as ElevenAgents.
- OpenAI Realtime API T1
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 integrate as one of their LLM choices.
- Pipecat (Daily) T1
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 compose with.
- Hume EVI T1
Hume's Empathic Voice Interface (EVI) — voice agent platform with vocal-affect understanding, using Hume's proprietary speech-prosody models. Hume will shut down the EVI and TTS APIs on 2026-11-13 (announced in its docs). Hume raised $50M Series B Mar-2024 (EQT).
Sources (46 cited facts, 5 third-party)
Each fact links to the page it came from; the badge says who published it (how to read sources).
- What it is Developer platform for AI voice agents (low-latency) vendor
- What it does & what's distinct Voice-agent platform with vendor focus on sub-800ms turn latency and proprietary voice m… vendor
- Claims / benefits YC S24; >$1M ARR by month 6; proprietary low-latency voice stack vendor
- Modalities voice (PSTN + WebRTC) + text vendor
- Created 2024 (YC S24) third-party
- GitHub github.com/RetellAI (SDKs only) repo
- Mindshare Often paired with Vapi in voice-AI comparisons; YC distribution vendor
- Funding $4.6M seed Aug-2024 (BoxGroup + others) third-party
- Customers / scale Production users in healthcare, e-commerce, recruiting; >$1M ARR month 6 vendor
- Pricing Pay-as-you-go $0.07-$0.31/min for voice agents (Retell voice infra $0.055/min plus TTS a… vendor
- Compliance SOC 2 Type II; HIPAA BAA vendor
- Data handling Recording opt-out; HIPAA BAA; PII redaction vendor
- Deployment Cloud-managed vendor
- HQ US (San Francisco; YC) third-party
- Founders / pedigree YC S24 team (CEO Shao + co-founders) third-party
- Memory volume / scale Vendor reports millions of minutes monthly vendor
- Performance <800ms turn latency per vendor benchmarks vendor
- API surface REST API + Python/JS/Go SDKs; webhooks vendor
- Latency p50/p99 <800ms turn-to-turn; <500ms with custom stack vendor
- Backend storage Call state in Retell-managed DB vendor
- Multi-tenancy Multi-tenant cloud vendor
- Encryption TLS + AES-256 vendor
- SSO / RBAC SSO on Enterprise vendor
- Versioning Agents versioned in dashboard vendor
- Tombstoning User-initiated delete vendor
- Namespace primitives per-workspace / per-agent vendor
- Forgetting policy Configurable retention vendor
- MCP support yes — agents can call MCP tools during live calls vendor
- Webhooks / events Webhooks for call events vendor
- Import / export Agent config JSON-exportable vendor
- Validated verticals healthcare, e-commerce, recruiting, real estate vendor
- Time to running <30min (sign-up + first agent) vendor
- Anti-fit Telephony focus; smaller funding than Vapi; per-minute pricing vendor
- Optimised for Sub-800ms voice turn latency with vertically-integrated stack vendor
- Adjacent infrastructure Twilio SIP; in-house STT/TTS; Anthropic / OpenAI LLMs vendor
- Pros Latency-first positioning; SOC 2 + HIPAA; YC distribution; clean SDKs. vendor
- Cons Smaller than Vapi; per-minute economics at scale; proprietary stack reduces flexibility. vendor
- Project & sources retellai.com; docs.retellai.com vendor
- adoption-accelerator yc-w24 third-party
- architecture-deployment-locus cloud vendor
- licensing-bucket commercial vendor
- positioning-platform-vs-product platform vendor
- taxonomy-three-layer-rollup agent-infra repo
- compliance-certifications gdpr,hipaa,iso27001,soc2-type2 vendor
- sdk-languages python,rest,typescript vendor
- protocol-support mcp-client,mcp-server vendor
What changed
Changes to this record's lifecycle, licence, release, pricing and hosting facts, from the catalog's git history. Subscribe (Atom)
- 2026-10-27
- Pricing “Per-minute usage ($0.07/min + provider passthrough)” → “Pay-as-you-go $0.07-$0.31/min for voice agents (Retell voice infra $0.055/min plus TTS and LLM components), $10 free credits, 20 concurrent calls included; Enterprise custom” source
- MCP support first recorded as “yes — agents can call MCP tools during live calls” source
Related systems
References (3)
- Anthropic Claude (foundation models) depends on at runtime — adjacent-infrastructure cell: Twilio SIP; in-house STT/TTS; Anthropic / OpenAI LLMs
- OpenAI GPT family (GPT-5 / GPT-4o / o3 / o4) depends on at runtime — adjacent-infrastructure cell: Twilio SIP; in-house STT/TTS; Anthropic / OpenAI LLMs
- Vapi competes with — Direct competitor to Vapi with proprietary-model focus.