Fixie

Fixie is the company behind Ultravox Realtime, a speech-native voice AI platform for building natural, low-latency conversational voice agents. Rather than transcribing speech to text first, Ultravox processes audio directly to preserve tone, cadence, and pitch while cutting latency. The Ultravox Realtime REST API (api.ultravox.ai) lets developers create reusable agents, start and manage calls, define custom and built-in tools, clone and manage voices, build RAG corpora, wire telephony (Twilio, Telnyx, Plivo, SIP), and subscribe to call-lifecycle webhooks. Client SDKs ship for JavaScript, Python, Flutter/Dart, React Native, Kotlin/Android, and Swift/iOS. Fixie was backed by Redpoint Ventures; fixie.ai now redirects to ultravox.ai and its open models are published under the fixie-ai organization on Hugging Face.

Fixie publishes 1 API on the APIs.io network: Ultravox Realtime API. Tagged areas include Company, Voice AI, Conversational AI, Real-time, and Speech.

The Fixie catalog on APIs.io includes 1 event-driven AsyncAPI specification.

Fixie’s developer surface includes changelog, documentation, API reference, getting-started guide, engineering blog, pricing, signup flow, and 16 more developer resources.

🌐 Visit website 📡 Source on GitHub
45.0/100 developing Agent 42/100 agent aware Full breakdown ↓
scored 2026-07-20 · rubric v0.4
1 APIs 1 MCP Servers 0 Features
CompanyVoice AIConversational AIReal-timeSpeechAgentsTelephonyMachine LearningSIPWebhooks

API Rating

API Evangelist API Evangelist Rating How this is scored →
scored 2026-07-20 · rubric v0.4
Composite quality — 45.0/100 · developing
Contract Quality 7.5 / 25
Developer Ergonomics 10.9 / 20
Commercial Clarity 10.5 / 20
Operational Transparency 6.8 / 13
Governance 0.0 / 12
Discoverability 9.3 / 10
Agent readiness — 42/100 · agent aware
Machine-Readable Contract 18 / 18
Agentic Access Contract 15 / 15
MCP Server 0 / 12
Machine-Readable Auth 0 / 10
Idempotency 0 / 9
Stable Error Semantics 0 / 8
Request/Response Examples 0 / 7
Rate-Limit Signaling 0 / 7
Typed Event Surface 6 / 6
Agent Skills 5 / 5
Well-Known Catalog 0 / 4
Consent & Bot Identity 0 / 3
Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/fixie: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

APIs

Ultravox Realtime API

Speech-native voice-agent REST API — create agents and calls, manage tools, voices, corpora (RAG), telephony/SIP configuration, and webhooks.

MCP Servers

fixie-mcp.yml

MCP SERVER

Event Specifications

Fixie Webhooks

ASYNCAPI

Resources

Get Started 4

Portal, sign-up, and the first successful call

DeveloperPortal
DeveloperPortal
 GettingStarted
GettingStarted
 SignUp
SignUp
 Login
Login

Documentation 2

Reference material describing how the API behaves

Documentation
Documentation
 APIReference
APIReference

Agent Surfaces 2

MCP servers, agent skills, and machine-readable catalogs

AgentSkill
AgentSkill
 LLMsTxt
LLMsTxt

Design & Contract 1

Pagination, idempotency, versioning, errors, and events

Webhooks
Webhooks

Build 3

SDKs, sample code, and the tooling you integrate with

Packages
Packages
 SDKs
SDKs
 GitHubOrganization
GitHubOrganization

Access & Security 2

Authentication, authorization, and security posture

DomainSecurity
DomainSecurity
 TrustCenter
TrustCenter

Operate 4

Status, limits, changes, and where to get help

ChangeLog
ChangeLog
 StatusPage
StatusPage
 Deprecation
Deprecation
 Support
Support

Commercial 3

Pricing, plans, and the legal terms of use

Pricing
Pricing
 TermsOfService
TermsOfService
 PrivacyPolicy
PrivacyPolicy

Company 2

The organization behind the API

Blog
Blog
 Website
Website

Source (apis.yml)

apis.yml Raw ↑ 
aid: fixie
name: Fixie
description: Fixie is the company behind Ultravox Realtime, a speech-native voice AI platform for building natural, low-latency
  conversational voice agents. Rather than transcribing speech to text first, Ultravox processes audio directly to preserve
  tone, cadence, and pitch while cutting latency. The Ultravox Realtime REST API (api.ultravox.ai) lets developers create
  reusable agents, start and manage calls, define custom and built-in tools, clone and manage voices, build RAG corpora, wire
  telephony (Twilio, Telnyx, Plivo, SIP), and subscribe to call-lifecycle webhooks. Client SDKs ship for JavaScript, Python,
  Flutter/Dart, React Native, Kotlin/Android, and Swift/iOS. Fixie was backed by Redpoint Ventures; fixie.ai now redirects
  to ultravox.ai and its open models are published under the fixie-ai organization on Hugging Face.
url: https://raw.githubusercontent.com/api-evangelist/fixie/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- redpoint-ventures
x-tier: profiled
x-tier-reason: enriched-from-public-api
specificationVersion: '0.20'
created: '2026-07-17'
modified: '2026-07-19'
image: https://raw.githubusercontent.com/api-evangelist/fixie/refs/heads/main/openapi/fixie-ultravox-openapi-original.yml
tags:
- Company
- Voice AI
- Conversational AI
- Real-time
- Speech
- Agents
- Telephony
- Machine Learning
- SIP
- Webhooks
apis:
- name: Ultravox Realtime API
  description: Speech-native voice-agent REST API — create agents and calls, manage tools, voices, corpora (RAG), telephony/SIP
    configuration, and webhooks.
  humanURL: https://docs.ultravox.ai/
  baseURL: https://api.ultravox.ai/api
  tags:
  - Voice AI
  - Real-time
  - Agents
  - Telephony
  properties:
  - type: OpenAPI
    url: openapi/fixie-ultravox-openapi-original.yml
  - type: Overlay
    url: overlays/fixie-ultravox-overlay.yaml
  - type: Authentication
    url: authentication/fixie-authentication.yml
  - type: AgenticAccess
    url: agentic-access/fixie-agentic-access.yml
  - type: MCPServer
    url: mcp/fixie-mcp.yml
  - type: Conventions
    url: conventions/fixie-conventions.yml
  - type: ErrorCatalog
    url: errors/fixie-problem-types.yml
  - type: Lifecycle
    url: lifecycle/fixie-lifecycle.yml
  - type: DataModel
    url: data-model/fixie-data-model.yml
  - type: Conformance
    url: conformance/fixie-conformance.yml
  - type: AsyncAPI
    url: asyncapi/fixie-webhooks.yml
  - type: Webhooks
    url: asyncapi/fixie-webhooks.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: DomainSecurity
  url: security/fixie-domain-security.yml
- type: TrustCenter
  url: security/fixie-trust-center.yml
- type: Packages
  url: packages/fixie-packages.yml
- type: SDKs
  url: packages/fixie-packages.yml
- type: ChangeLog
  url: changelog/fixie-changelog.yml
- type: AgentSkill
  url: skills/_index.yml
- type: LLMsTxt
  url: llms/fixie-llms.txt
- type: StatusPage
  url: https://status.ultravox.ai
- type: Deprecation
  url: https://docs.ultravox.ai/changelog/deprecation
- type: Webhooks
  url: asyncapi/fixie-webhooks.yml
- type: DeveloperPortal
  url: https://docs.ultravox.ai/
- type: Documentation
  url: https://docs.ultravox.ai/
- type: APIReference
  url: https://docs.ultravox.ai/api-reference
- type: GettingStarted
  url: https://docs.ultravox.ai/gettingstarted/quickstart/agent-console
- type: GitHubOrganization
  url: https://github.com/fixie-ai
- type: Blog
  url: https://ultravox.ai/blog
- type: Pricing
  url: https://ultravox.ai/pricing
- type: SignUp
  url: https://app.ultravox.ai
- type: Login
  url: https://app.ultravox.ai
- type: TermsOfService
  url: https://ultravox.ai/terms
- type: PrivacyPolicy
  url: https://ultravox.ai/privacy
- type: Support
  url: mailto:hello@ultravox.ai
- type: Website
  url: https://ultravox.ai/
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence