Features, pricing, and fit
Compare Sierra Agent and Ultravox on voice capabilities, pricing, and fit.
Compare Sierra Agent and Ultravox for AI phone agents, then match channels, workflows, and deployment models to your call flow.
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.
API-first native speech-language model with a no-code Console, custom tools, and bring-your-own telephony for phone, web, and native apps.
Engineering teams that want direct speech processing and control over telephony or app transports.
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
Sierra Agent: Outcome-based pricing tied to agreed results; Sierra also describes blended consumption pricing for routing or greeter interactions. Ultravox: Pay-as-you-go and Pro plans combine a published per-minute rate with monthly plan fees; Enterprise is custom, and SIP is priced separately. 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 Sierra Agent include Not publicly documented. For Ultravox, 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: Sierra Agent: Public voice detail is limited. Confirm telephony, transfer, recording, retention, language, and exact billable outcome. Ultravox: Open weights do not remove hosting, latency, safety, evaluation, voice, and telephony work. Review license and SLA.
Record your requirements and pilot results in the buyer worksheet →
Swipe or scroll the table to see every column.
| Criterion | Sierra Agent | Ultravox |
|---|---|---|
| Provider type | Enterprise customer-service agent platform | Native speech-language model API |
| Best fit | CX organizations that want one agent model across voice and digital channels with brand-persona controls. | Engineering teams that want direct speech processing and control over telephony or app transports. |
| Key capabilities | conversations; backend actions; guardrails; analytics; multi-channel deployment | direct speech-language interaction; open weights; hosted API; tools; realtime sessions |
| Team sizes | enterprise | startup; mid-market; enterprise; developer |
| Call surfaces | voice; chat; digital customer service | phone / PSTN; API / SDK |
| Voice stack | Not publicly documented | Native speech-language model |
| Telephony | Not publicly documented | 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 | Outcome-based pricing tied to agreed results; Sierra also describes blended consumption pricing for routing or greeter interactions. | Pay-as-you-go and Pro plans combine a published per-minute rate with monthly plan fees; Enterprise is custom, and SIP is priced separately. |
| Pricing signal | Outcome-based enterprise pricing; no public rate. | 30 free minutes; $0.05/min pay-as-you-go; Pro $100/month; SIP about $0.005/min. |
| Free plan or trial | Not publicly documented | 30 free minutes; open weights under published license. |
| What stands out | 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. | Ultravox documents a native speech path without a separate ASR stage, then exposes both Console prototyping and REST/SDK integration with BYOT telephony. |
| Considerations | Public voice detail is limited. Confirm telephony, transfer, recording, retention, language, and exact billable outcome. | Open weights do not remove hosting, latency, safety, evaluation, voice, and telephony work. Review license and SLA. |
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.
Engineering teams that want direct speech processing and control over telephony or app transports.
Ultravox documents a native speech path without a separate ASR stage, then exposes both Console prototyping and REST/SDK integration with BYOT telephony.
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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