Features, pricing, and fit
Compare ConversationRelay and Ultravox on voice capabilities, pricing, and fit.
Compare Twilio ConversationRelay and Ultravox for AI phone agents, Voice AI platforms, then match channels, workflows, and deployment models to your call flow.
Programmable Voice component that connects a TwiML ConversationRelay session to an application WebSocket for STT/TTS, language settings, DTMF, and call events.
Developers building their own voice-agent logic while keeping telephony, media handling, and call control in Twilio.
Explore its buying criteria: AI phone agents · Voice AI platforms.
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
Twilio ConversationRelay: Usage-based Programmable Voice minutes and phone numbers, plus ConversationRelay per-minute charges; model, provider, and other call features are separate. 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 Twilio ConversationRelay 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: Twilio ConversationRelay: Not a packaged agent. Region, carrier, recording, compliance, model, and application responsibilities remain with the implementer. 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 | ConversationRelay | Ultravox |
|---|---|---|
| Provider type | Telephony voice-agent runtime | Native speech-language model API |
| Best fit | Developers building their own voice-agent logic while keeping telephony, media handling, and call control in Twilio. | Engineering teams that want direct speech processing and control over telephony or app transports. |
| Key capabilities | phone audio streaming; speech interface; interruptions; WebSocket protocol; TwiML controls | direct speech-language interaction; open weights; hosted API; tools; realtime sessions |
| Team sizes | startup; mid-market; enterprise; developer | startup; mid-market; enterprise; developer |
| Call surfaces | phone / PSTN; WebSocket | phone / PSTN; API / SDK |
| Voice stack | Cascaded speech interface with developer-supplied LLM | Native speech-language model |
| Telephony | Twilio Programmable Voice; phone numbers; SIP | 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 | Usage-based Programmable Voice minutes and phone numbers, plus ConversationRelay per-minute charges; model, provider, and other call features are separate. | 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 | ConversationRelay $0.07/min; US local outbound $0.014, inbound $0.0085, SIP $0.004, number $1.15/month. | 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 | ConversationRelay handles the live call’s STT/TTS and session transport, then sends prompts, audio-control events, and optional DTMF over a required secure WebSocket to the application. | Ultravox documents a native speech path without a separate ASR stage, then exposes both Console prototyping and REST/SDK integration with BYOT telephony. |
| Considerations | Not a packaged agent. Region, carrier, recording, compliance, model, and application responsibilities remain with the implementer. | Open weights do not remove hosting, latency, safety, evaluation, voice, and telephony work. Review license and SLA. |
Developers building their own voice-agent logic while keeping telephony, media handling, and call control in Twilio.
ConversationRelay handles the live call’s STT/TTS and session transport, then sends prompts, audio-control events, and optional DTMF over a required secure WebSocket to the application.
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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