Features, pricing, and fit
Compare Realtime API and Sierra Agent on voice capabilities, pricing, and fit.
Compare OpenAI Realtime and Sierra Agent for AI phone agents, then match channels, workflows, and deployment models to your call flow.
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.
Customer-service agent platform for inbound/outbound voice, messaging, email, live assist, and ChatGPT channel publishing.
CX organizations that want one agent model across voice and digital channels with brand-persona controls.
Explore its buying criteria: AI phone agents · Contact-center AI.
Both profiles checked 2026-09-04.
Use the table below to compare each provider’s documented scope.
Before you decide
OpenAI Realtime: Token-based API pricing for text, audio, and image modalities; audio input/output rates are published per million tokens. Sierra Agent: Outcome-based pricing tied to agreed results; Sierra also describes blended consumption pricing for routing or greeter interactions. 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 OpenAI Realtime include Not publicly documented. For Sierra Agent, 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: OpenAI Realtime: Not a turnkey contact center. Implement telephony operations, identity, tools, monitoring, evaluation, retention, and escalation. Sierra Agent: Public voice detail is limited. Confirm telephony, transfer, recording, retention, language, and exact billable outcome.
Record your requirements and pilot results in the buyer worksheet →
Swipe or scroll the table to see every column.
| Criterion | Realtime API | Sierra Agent |
|---|---|---|
| Provider type | Native realtime multimodal model API | Enterprise customer-service agent platform |
| Best fit | Product and engineering teams building a spoken application around a realtime model instead of a packaged contact-center product. | CX organizations that want one agent model across voice and digital channels with brand-persona controls. |
| Key capabilities | audio-to-audio conversation; WebRTC; WebSocket; SIP; tools | conversations; backend actions; guardrails; analytics; multi-channel deployment |
| Team sizes | startup; mid-market; enterprise; developer | enterprise |
| Call surfaces | WebRTC; WebSocket; SIP; API / SDK | voice; chat; digital customer service |
| Voice stack | Native audio input/output with tool calling | Not publicly documented |
| Telephony | SIP connection; carrier integration remains buyer responsibility | Not publicly documented |
| 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 | Token-based API pricing for text, audio, and image modalities; audio input/output rates are published per million tokens. | Outcome-based pricing tied to agreed results; Sierra also describes blended consumption pricing for routing or greeter interactions. |
| Pricing signal | GPT-Realtime audio $32 per million input audio tokens and $64 per million output audio tokens. | Outcome-based enterprise pricing; no public rate. |
| Free plan or trial | Not publicly documented | Not publicly documented |
| What stands out | GPT-Realtime accepts and returns audio directly, while the Agents SDK supplies transport helpers plus tools, guardrails, handoffs, and session history. | Sierra pairs channel-spanning agents and configurable Voice Personas with an outcome-based commercial model whose billing is tied to agreed task results; routing/greeter cases may use consumption pricing. |
| Considerations | Not a turnkey contact center. Implement telephony operations, identity, tools, monitoring, evaluation, retention, and escalation. | Public voice detail is limited. Confirm telephony, transfer, recording, retention, language, and exact billable outcome. |
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.
CX organizations that want one agent model across voice and digital channels with brand-persona controls.
Sierra pairs channel-spanning agents and configurable Voice Personas with an outcome-based commercial model whose billing is tied to agreed task results; routing/greeter cases may use consumption pricing.
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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