Features, pricing, and fit
Compare Line and Realtime API on voice capabilities, pricing, and fit.
Compare Cartesia Line and OpenAI Realtime for AI phone agents, Voice AI platforms, then match channels, workflows, and deployment models to your call flow.
Managed Line runtime for voice agents with no-code Agent Builder, SDK-defined reasoning, Cartesia Ink STT, Sonic TTS, deployment, and observability.
Teams that want managed audio plumbing while retaining code-level control over reasoning, tools, and external APIs.
Explore its buying criteria: AI phone agents · Voice AI platforms.
Model-level realtime API for text and audio input/output over WebRTC, WebSocket, or SIP, with function calling.
Product and engineering teams building a spoken application around a realtime model instead of a packaged contact-center product.
Explore its buying criteria: AI phone agents · Voice AI platforms.
Both profiles checked 2026-09-04.
Use the table below to compare each provider’s documented scope.
Before you decide
Cartesia Line: Not publicly documented OpenAI Realtime: Token-based API pricing for text, audio, and image modalities; audio input/output rates are published per million tokens. Ask both vendors to quote the same expected workload, required channels, and implementation scope. Include required subscriptions and usage charges before comparing the total; the listed starting prices alone may cover different work.
The recorded knowledge and data sources for Cartesia Line include Not publicly documented. For OpenAI Realtime, they include Not publicly documented. Ask each provider to demonstrate access for the exact systems you use, with permissions, freshness, and failure behavior. A source missing from this directory is not proof that a provider cannot support it.
Use the same representative calls, approved instructions, and escalation rules in both pilots. How does it handle interruption and uncertainty? Which actions can it complete, and which require approval? What context reaches a human during transfer? Record conversation quality, completed tasks, human handoffs, and total cost in the buyer worksheet. Check these specific cautions before launch: Cartesia Line: Confirm product availability, carrier coverage, models, data handling, and generally available features. OpenAI Realtime: Not a turnkey contact center. Implement telephony operations, identity, tools, monitoring, evaluation, retention, and escalation.
Record your requirements and pilot results in the buyer worksheet →
Swipe or scroll the table to see every column.
| Criterion | Line | Realtime API |
|---|---|---|
| Provider type | Voice agent platform and speech API | Native realtime multimodal model API |
| Best fit | Teams that want managed audio plumbing while retaining code-level control over reasoning, tools, and external APIs. | Product and engineering teams building a spoken application around a realtime model instead of a packaged contact-center product. |
| Key capabilities | realtime voices; agent configuration; telephony; tools; API | audio-to-audio conversation; WebRTC; WebSocket; SIP; tools |
| Team sizes | startup; mid-market; enterprise; developer | startup; mid-market; enterprise; developer |
| Call surfaces | phone / PSTN; API / SDK | WebRTC; WebSocket; SIP; API / SDK |
| Voice stack | Cascaded STT-LLM-TTS using Cartesia TTS | Native audio input/output with tool calling |
| Telephony | Not publicly documented | SIP connection; carrier integration remains buyer responsibility |
| Call controls | Not publicly documented | Not publicly documented |
| Languages | Not publicly documented | Not publicly documented |
| Integrations | Not publicly documented | Not publicly documented |
| Knowledge and data | Not publicly documented | Not publicly documented |
| Pricing model | Not publicly documented | Token-based API pricing for text, audio, and image modalities; audio input/output rates are published per million tokens. |
| Pricing signal | Approximately $0.06/min plus about $0.014/min managed telephony; verify current calculator. | GPT-Realtime audio $32 per million input audio tokens and $64 per million output audio tokens. |
| Free plan or trial | Not publicly documented | Not publicly documented |
| What stands out | Line separates reasoning from audio operations: it offers a no-code builder or SDK for custom logic while managing deployment/observability and pairing Ink with Sonic. | GPT-Realtime accepts and returns audio directly, while the Agents SDK supplies transport helpers plus tools, guardrails, handoffs, and session history. |
| Considerations | Confirm product availability, carrier coverage, models, data handling, and generally available features. | Not a turnkey contact center. Implement telephony operations, identity, tools, monitoring, evaluation, retention, and escalation. |
Teams that want managed audio plumbing while retaining code-level control over reasoning, tools, and external APIs.
Line separates reasoning from audio operations: it offers a no-code builder or SDK for custom logic while managing deployment/observability and pairing Ink with Sonic.
Product and engineering teams building a spoken application around a realtime model instead of a packaged contact-center product.
GPT-Realtime accepts and returns audio directly, while the Agents SDK supplies transport helpers plus tools, guardrails, handoffs, and session history.
Verify current pricing, limits, security, and required integrations directly with each provider before purchasing.
Test recognition, speech quality, interruptions, language switching, tool use, and human transfer with your own calls in the required language. Availability can vary by model, plan, and phone route.
DocsBot documents multilingual voice workflows and Japanese support. Verify the exact voice, phone path, and transfer behavior in your pilot. Review DocsBot language information ↗
Other providers’ language claims reflect cited vendor material; confirm Japanese and other required languages directly with each provider.
Listing does not imply endorsement or a performance guarantee. This directory is published by DocsBot. Editorial policy
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