# Voice Agent APIs for Developers

> Source: https://theagentsindex.com/collections/voice-agent-apis (curated, quality-gated, re-verified)

This collection rounds up the voice agent platforms in our index that expose a programmatic integration surface to developers. Each tool here ships with a real interface, whether a REST endpoint, a WebSocket, an SDK, an MCP server or an equivalent, so you can wire its voice layer into your own product rather than only use the vendor's hosted console. Voice-only consumer products, no-API receptionists, and platforms that require a sales call before publishing any integration surface are excluded. The same voice model, behind a real developer API, qualifies; a great voice that ships without one does not.

| Name | What it is | Why it's here | Pricing | API |
| --- | --- | --- | --- | --- |
| [Bland](https://theagentsindex.com/bland-ai.md) | Enterprise voice AI platform for inbound and outbound phone agents, running on Bland's own self-hosted models. | Enterprise voice AI that owns its own model stack, priced all-in per minute with no model pass-throughs, and ships a public API for embedding per-minute voice agents into a third-party product. | — | Yes |
| [Deepgram Voice Agent API](https://theagentsindex.com/deepgram-voice-agent-api.md) | One WebSocket API that runs speech-to-text, LLM orchestration and text-to-speech for real-time voice agents. | The speech-infrastructure vendor's own voice-agent product: a single WebSocket drives managed STT, LLM and TTS, with six named LLM providers and a flat $4.50/hr rate. | — | Yes |
| [ElevenLabs Agents](https://theagentsindex.com/elevenlabs-conversational-ai.md) | Hosted platform for building voice and chat agents, with telephony, SDKs and a choice of LLM. | The voice-quality specialist's own agent layer, with a developer API exposing 10,000+ voices, instant cloning, and a bring-your-own-LLM brain behind it. | — | Yes |
| [OpenAI Realtime API](https://theagentsindex.com/openai-realtime-api.md) | OpenAI's speech-to-speech API for low-latency voice agents over WebRTC, WebSocket or SIP. | OpenAI's own speech-to-speech model API for voice agents, reachable over WebRTC, WebSocket, or native SIP telephony, billed purely on audio tokens with no platform fee. | — | Yes |
| [PolyAI](https://theagentsindex.com/polyai.md) | Enterprise platform for building voice and chat agents that resolve customer calls, priced per minute. | The pre-LLM-era enterprise voice AI incumbent ($750M-valued, 200+ enterprise customers); pricing returned to sales-led in May 2026 after a public signup tier was removed, with studio.poly.ai as the still-resolving self-serve surface for building and embedding voice agents rather than self-serve API keys. | — | Yes |
| [Retell AI](https://theagentsindex.com/retell-ai.md) | Pay-as-you-go platform for building, testing and running AI phone, chat and SMS agents. | Phone-call voice agents built on Retell's turn-taking layer, with a public API to plug in your own LLM, voice, and telephony, shippable over voice, chat or SMS. | — | Yes |
| [Synthflow](https://theagentsindex.com/synthflow-ai.md) | Enterprise voice AI platform with in-house telephony for inbound and outbound call automation. | A no-code voice AI platform for enterprise phone agents, with a visual Flow Designer and a developer API exposed alongside the hosted build surface. | — | Yes |
| [Cartesia](https://theagentsindex.com/cartesia.md) | Real-time speech models and a managed runtime for production phone and web voice agents. | Line, Cartesia's voice-agent SDK, is Apache-2.0 with no caveat; ships as both an open SDK and a published API, the only Apache-licensed open-source voice-agent entry that does so. | — | Yes |
| [LiveKit Agents](https://theagentsindex.com/livekit-agents.md) | Open-source Python and Node.js framework for voice AI agents, with LiveKit Cloud hosting, telephony and observability. | Apache 2.0 voice-agent framework with 13.1k GitHub stars, self-hostable, with a documented API surface and the only open-source voice-agent pick with fully published pricing. | — | Yes |

## How this list is built

A tool earns a place here when its own Published, sourced listing names a programmatic integration surface a developer can call: a REST or GraphQL endpoint, a WebSocket, an SDK in at least one general-purpose language, an MCP server, or an equivalent open protocol. The API must be documented and reachable without a sales call. A "contact us" enterprise tier with no self-serve surface named anywhere in the listing does not qualify on its own. Voice-only consumer products that ship without a developer API are out, even where the underlying model is identical. Self-hosted open-source voice frameworks and hosted platforms are both included when each ships an API a developer can call; pricing model, rate limits and self-serve vs. sales-led onboarding vary entry by entry. Membership is re-checked against each listing's own already-researched, quality-gated fields rather than the `voice-agents` and `api` tags in isolation.