Features, pricing, and fit
Compare ConversationRelay and Empathic Voice Interface on voice capabilities, pricing, and fit.
Compare Twilio ConversationRelay and Hume EVI 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.
EVI is a speech-to-speech WebSocket API that streams transcripts, vocal-expression measures, assistant text, and response audio.
Developers evaluating prosody-aware spoken interactions with configurable voices and optional supplemental LLMs.
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. Hume EVI: Monthly plans include EVI minutes; additional EVI 3 usage is billed per minute on Pro, Scale, and Business, while TTS uses separate character allowances and rates. 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 Hume EVI, 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. Hume EVI: Empathic positioning is not proof of accurate emotion inference. Test false interpretations, cultural variation, consent, sensitive uses, and escalation.
Record your requirements and pilot results in the buyer worksheet →
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| Criterion | ConversationRelay | Empathic Voice Interface |
|---|---|---|
| Provider type | Telephony voice-agent runtime | Expressive native voice model API |
| Best fit | Developers building their own voice-agent logic while keeping telephony, media handling, and call control in Twilio. | Developers evaluating prosody-aware spoken interactions with configurable voices and optional supplemental LLMs. |
| Key capabilities | phone audio streaming; speech interface; interruptions; WebSocket protocol; TwiML controls | prosody-aware interaction; expressive output; realtime sessions; tools |
| Team sizes | startup; mid-market; enterprise; developer | startup; mid-market; enterprise; developer |
| Call surfaces | phone / PSTN; WebSocket | WebSocket; web; mobile; telephony integrations |
| Voice stack | Cascaded speech interface with developer-supplied LLM | Native speech-to-speech with prosody-sensitive processing |
| 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. | Monthly plans include EVI minutes; additional EVI 3 usage is billed per minute on Pro, Scale, and Business, while TTS uses separate character allowances and rates. |
| Pricing signal | ConversationRelay $0.07/min; US local outbound $0.014, inbound $0.0085, SIP $0.004, number $1.15/month. | EVI 3: Pro $70/month with 1,200 minutes and $0.06/min additional; Scale $200 with 5,000 and $0.05; Business $500 with 12,500 and $0.04. |
| Free plan or trial | Not publicly documented | Free plan includes 5 EVI minutes; confirm the selected EVI version and current terms. |
| 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. | EVI’s structured WebSocket messages expose both transcript and vocal-expression measures alongside generated text/audio; EVI versions differ in language coverage and supplemental-LLM requirements. |
| Considerations | Not a packaged agent. Region, carrier, recording, compliance, model, and application responsibilities remain with the implementer. | Empathic positioning is not proof of accurate emotion inference. Test false interpretations, cultural variation, consent, sensitive uses, and escalation. |
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.
Developers evaluating prosody-aware spoken interactions with configurable voices and optional supplemental LLMs.
EVI’s structured WebSocket messages expose both transcript and vocal-expression measures alongside generated text/audio; EVI versions differ in language coverage and supplemental-LLM requirements.
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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