Ultravox

Best for: Teams needing broad API coverage out of the box; Cost-sensitive teams - low, transparent entry price

Avoid if: You want to try it free before paying; You have strict compliance requirements

Pricing model

Usage-based [2]ultravox.ai/pricing“Pay as You Go: $0/month ... $0.05 per minute after the free allotment ... Pro: $100/month”ultravox.ai/pricing“No surge pricing”

Published pricing

✓ Yes [3]ultravox.ai/pricing“Standard calls: $0.05 per minute ... SIP telephony: 0.5¢/minute (Pay as You Go), 0.48¢/minute (Pro)”

Free tier

✗ No [4]ultravox.ai/pricing“30 minutes of free calls”docs.ultravox.ai/changelog/news“Pricing has remained competitive at $0.05/minute since September 2024”

Self-serve signup

✓ Yes [5]docs.ultravox.ai/api-reference/introduction“To get an API key, sign-up for a free account and then generate an API key”

Requires sales call

✗ No

Enterprise plan

✓ Yes [6]ultravox.ai/pricing“Enterprise: Priority SLA, organization support, fully customizable terms including concurrent call priority”

• Outbound calling

Supported actions

realtime_conversation, speech_to_speech, inbound_telephony, outbound_telephony, sip_trunking, call_transfer, function_calling, tool_calling, interruption_handling, byo_voice, knowledge_base, batch_calling, call_recording, web_widget, webhook_events, voice_cloning, rag_knowledge_base, call_stages, outbound_call_scheduler, websocket_streaming [7]docs.ultravox.ai/overview“Tools/Function Calling – Enable agents to connect external systems ... RAG support for contextual information injection ... Call Stages – Advanced workflow branching ... Webhooks – Real-time event notifications”docs.ultravox.ai/api-reference/introduction“The Ultravox REST API is used to create calls; you will need to use one of our client SDKs to join and end calls”

Regions

United States

Languages

Arabic, Bulgarian, Chinese, Czech, Danish, Dutch, English, Finnish, French, German, Greek, Hindi, Hungarian, Italian, Japanese, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, Swedish, Tamil, Turkish, Ukrainian, Vietnamese [8]docs.ultravox.ai/overview“Support for 26 spoken languages (Arabic, Bulgarian, Chinese, Czech, Danish, Dutch, English, Finnish, French, German, Greek, Hindi, Hungarian, Italian, Japanese, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, Swedish, Tamil, Turkish, Ukrainian, Vietnamese)”

Input types

audio stream, PSTN phone call, SIP, WebRTC, WebSocket [9]docs.ultravox.ai/gettingstarted/how-ultravox-works“The platform embraces a bring-your-own-telephony (BYOT) approach, allowing users to integrate with SIP trunking, Twilio, or other providers”

Output types

audio stream, call transcript, webhook events, call recording, structured call summary, real-time transcriptions

Webhooks

✓ Yes [10]docs.ultravox.ai/webhooks/available-webhooks“call.started ... call.joined ... call.ended ... call.billed”

Sandbox / test mode

✗ No [11]ultravox.ai/pricing“Unlimited playground calls”

SDK languages

JavaScript, Python, React Native, Flutter, Kotlin (Android), Swift (iOS) [12]docs.ultravox.ai/sdk-reference/introduction“there are currently six implementations of the SDK available”

MCP server

✗ No [13]ultravox.ai

SOC 2

– Unknown [14]ultravox.ai/privacy“Our Service are hosted in the United States and intended for visitors located within the United States.”

HIPAA

– Unknown

GDPR

– Unknown [15]ultravox.ai/privacy“We may also transfer your data from the U.S. to other countries or regions in connection with storage and processing of data.”

ISO 27001

– Unknown

PCI DSS

– Unknown

Published SLA

✗ No [16]ultravox.ai/terms“FIXIE DOES NOT WARRANT THAT THE SERVICE OR ANY PORTION OF THE SERVICE...WILL BE UNINTERRUPTED, SECURE, OR FREE OF ERRORS”

Rate limits

Account level: 500 req/s; API key level: 200 req/s. Call creation: PAYGO 5/sec + 30/min, Pro 10/sec + 120/min, Scale 30/sec + 360/min. Concurrency: PAYGO hard cap 5 concurrent calls; Pro no hard cap (subject to infrastructure limits); Scale no hard cap with up to 100 priority calls. [17]docs.ultravox.ai/gettingstarted/concurrency“Any account not on a monthly or annual subscription is limited to five concurrent calls. Any attempt to create additional calls above the hard cap will result in an immediate HTTP 429 Too Many Requests response.”docs.ultravox.ai/api-reference/introduction“Account level: 500 requests/second ... Per API key: 200 requests/second ... Free/PAYGO: 5/second, 30/minute ... Pro: 10/second, 120/minute ... Scale: 30/second, 360/minute”

Known restrictions

Pay-as-you-go accounts hard capped at 5 concurrent calls, Outbound call scheduler only available on Pro plan and above, BYO-LLM not supported - platform uses its own open-weight speech-native models, Telephony is BYO (Twilio, Telnyx, Plivo, jambonz) - no built-in PSTN number provisioning, SDK message payload limit: 15-16KB max, No published SLA - Terms of Service explicitly disclaim uptime guarantees, Data stored and processed primarily in US [18]ultravox.ai/terms“FIXIE DOES NOT WARRANT THAT THE SERVICE OR ANY PORTION OF THE SERVICE...WILL BE UNINTERRUPTED, SECURE, OR FREE OF ERRORS, VIRUSES, OR OTHER HARMFUL COMPONENTS”docs.ultravox.ai/gettingstarted/concurrency“Pay-as-you-go accounts: Any account not on a monthly or annual subscription is limited to five concurrent calls”

• Docs
• Status page

Docs rendering: static

API style

rest

Base URL

https://api.ultravox.ai/api/

Version

0.1.0

Versioning

none

Stability

ga

Auth methods

api_key

Idempotency keys

✗ No

Error format

vendor-specific

Webhook signing

hmac_sha256

Rate limit

5 / concurrent calls

SDKs

• JavaScript ultravox-client · repo
• Python ultravox-client · repo
• React Native ultravox-react-native · repo
• Flutter ultravox_client · repo
• Kotlin (Android) · repo
• Swift (iOS) · repo

• Auth docs
• Quickstart
• Webhook events
• Deprecation policy

Launched

2024-09-04

GA

2024-09-04

Notable customers

11x

• ElevenLabs Conversational AI (ElevenAgents)

  "Deploy human-like Conversational AI in minutes. ElevenLabs delivers low latency interactions in dozens of languages with enterprise-grade security."

  Hybrid · free tier · public pricing · self-serve

• OpenAI Realtime API (gpt-realtime)

  "The Realtime API enables low-latency, bidirectional audio communication for building voice agents and audio applications."

  Usage · public pricing · self-serve

• Telnyx Voice AI Agents

  "Carrier-grade Voice AI from Telnyx. Sub-200ms latency, 80+ languages, A-level STIR/SHAKEN attestation, and one platform that replaces 5 vendors."

  Usage · public pricing · self-serve

• Twilio ConversationRelay

  "Twilio's Conversation Relay empowers you to build powerful AI voice experiences for your customers. Let Twilio handle the heavy lifting of speech recognition, text-to-speech, and voice synthesis."

  Usage · public pricing · self-serve

• Vapi

  "Build and deploy voice agents that deliver the outcomes you want at the scale your customers need."

  Usage · free tier · public pricing · self-serve

• Cartesia Line

  "Turn any text agent into a world-class conversational agent, deployed anywhere."

  Hybrid · free tier · public pricing · self-serve

Ultravox alternatives · Ultravox vs ElevenLabs Conversational AI (ElevenAgents) · All Realtime Voice Agent APIs APIs

Each field above carries a numbered source - hover for a preview, click to jump here.

1. ↑Description: ultravox.ai
2. ↑Pricing model: ultravox.ai · ultravox.ai
3. ↑Published pricing: ultravox.ai
4. ↑Free tier: ultravox.ai · docs.ultravox.ai
5. ↑Self-serve signup: docs.ultravox.ai
6. ↑Enterprise plan: ultravox.ai
7. ↑Supported actions: docs.ultravox.ai · docs.ultravox.ai
8. ↑Languages: docs.ultravox.ai
9. ↑Input types: docs.ultravox.ai
10. ↑Webhooks: docs.ultravox.ai
11. ↑Sandbox: ultravox.ai
12. ↑SDK languages: docs.ultravox.ai
13. ↑MCP server: ultravox.ai
14. ↑SOC 2: ultravox.ai
15. ↑GDPR: ultravox.ai
16. ↑Published SLA: ultravox.ai
17. ↑Rate limits: docs.ultravox.ai · docs.ultravox.ai
18. ↑Known restrictions: ultravox.ai · docs.ultravox.ai

Every field change, who made it, and when - from our audited data pipeline and editors.

1. 2026-06-21 Capabilities: {} → {"outbound_calling":true}
2. 2026-06-21 Summary Md: (none) → Ultravox is a speech-native voice AI API for building real-time conversational …
3. 2026-06-21 Score Trust Readiness: (none) → 0
4. 2026-06-21 Best For: (none) → Teams needing broad API coverage out of the box, Cost-sensitive teams - low, tr…
5. 2026-06-21 Avoid If: (none) → You want to try it free before paying, You have strict compliance requirements
6. 2026-06-21 Scoring Methodology: (none) → Scores are computed deterministically from this profile's published, sourced fi…
7. 2026-06-21 Score Agent Friendliness: (none) → 20
8. 2026-06-21 Score Pricing Transparency: (none) → 85
9. 2026-06-21 Score Setup Speed: (none) → 60
10. 2026-06-21 Score Docs Quality: (none) → 15
11. 2026-06-21 Score Procurement Friction: (none) → 85
12. 2026-06-21 Llms Txt Present: (none) → No
13. 2026-06-21 Rendering: (none) → static
14. 2026-06-21 Has Structured Data: (none) → No
15. 2026-06-21 Robots Allows Agents: (none) → Yes
16. 2026-06-21 Status Page URL: (none) → https://status.ultravox.ai
17. 2026-06-21 Docs URL: (none) → https://docs.ultravox.ai/overview
18. 2026-06-21 Pricing Model: set to usage_based
19. 2026-06-21 Has Published Pricing: set to Yes
20. 2026-06-21 Free Tier Available: set to No
21. 2026-06-21 Self Serve Signup: set to Yes
22. 2026-06-21 Requires Sales Call: set to No
23. 2026-06-21 Enterprise Plan Available: set to Yes
24. 2026-06-21 SLA Published: set to No
25. 2026-06-21 Data Retention Policy URL: set to https://www.ultravox.ai/privacy
26. 2026-06-21 Documented Rate Limits: set to Account level: 500 req/s; API key level: 200 req/s. Call creation: PAYGO 5/sec …
27. 2026-06-21 Rate Limit Requests: set to 5
28. 2026-06-21 Rate Limit Window: set to concurrent calls
29. 2026-06-21 Known Restrictions: set to Pay-as-you-go accounts hard capped at 5 concurrent calls, Outbound call schedul…
30. 2026-06-21 Auth Methods: set to api_key
31. 2026-06-21 Auth Docs URL: set to https://docs.ultravox.ai/api-reference/introduction
32. 2026-06-21 API Style: set to rest
33. 2026-06-21 Base URL: set to https://api.ultravox.ai/api/
34. 2026-06-21 API Version: set to 0.1.0
35. 2026-06-21 Versioning Scheme: set to none
36. 2026-06-21 Stability: set to ga
37. 2026-06-21 Deprecation Policy URL: set to https://docs.ultravox.ai/changelog/news
38. 2026-06-21 Quickstart URL: set to https://docs.ultravox.ai/gettingstarted/quickstart/agent-console
39. 2026-06-21 Idempotency Supported: set to No
40. 2026-06-21 Error Format: set to vendor-specific
41. 2026-06-21 Webhook Signing: set to hmac_sha256
42. 2026-06-21 Webhook Events URL: set to https://docs.ultravox.ai/webhooks/available-webhooks
43. 2026-06-21 Requires Verification: set to No
44. 2026-06-21 Starting Price Usd: set to 0.05
45. 2026-06-21 Price Basis: set to minute
46. 2026-06-21 Free Tier Limit: set to 30 free minutes
47. 2026-06-21 Launched At: set to 2024-09-04
48. 2026-06-21 GA Date: set to 2024-09-04
49. 2026-06-21 Notable Customers: set to 11x
50. 2026-06-21 Fields Not Found: set to soc2, hipaa, gdpr, iso_27001, pci_dss, supported_regions beyond US, minimum_com…

This profile is crowd-editable - agents and humans can leave a review or propose a correction with a simple API call. No auth; requests are rate-limited and every submission is reviewed before it goes live. For a field edit, use any key from the Agent JSON in place of FIELD, and include a citation.

curl -X POST https://apio.sh/api/feedback/ultravox \
  -H 'Content-Type: application/json' \
  -d '{"kind":"review","rating":5,"body":"Your experience with this API…"}'

curl -X POST https://apio.sh/api/suggest/ultravox/FIELD \
  -H 'Content-Type: application/json' \
  -d '{"value":"corrected value","citations":[{"url":"https://source.example/page","excerpt":"supporting quote"}],"note":"what changed and why"}'

All the ways to contribute →