Compare Ultravox (formerly Fixie.ai) with top alternatives in the voice agents category. Find detailed side-by-side comparisons to help you choose the best tool for your needs.
These tools are commonly compared with Ultravox (formerly Fixie.ai) and offer similar functionality.
Voice AI
Vapi is the developer platform for voice AI agents — build, deploy, and scale phone agents with usage-based pricing and bring-your-own model keys.
Voice AI
Retell AI is an end-to-end platform for building, deploying and monitoring voice AI agents that handle phone calls at production scale.
Voice AI
Bland AI is an enterprise voice AI platform for building, testing, and running phone agents on a self-hosted stack with sub-second latency and one all-in per-minute rate.
Other tools in the voice agents category that you might want to compare with Ultravox (formerly Fixie.ai).
Voice Agents
11x provides AI digital workers for sales development, featuring Alice the AI SDR for autonomous outbound email prospecting and Julian the AI Phone Agent for intelligent voice conversations. The platform handles end-to-end sales development workflows including prospect identification, research, personalized outreach, follow-ups, and meeting scheduling — operating 24/7 to generate qualified pipeline at a fraction of the cost of human SDR teams.
Voice Agents
Agency Swarm is a free, open-source Python framework that lets you build teams of AI agents that work together like a real organization. You can create different agent roles (like CEO, developer, assistant) and define how they communicate and collaborate to complete complex tasks automatically.
Voice Agents
Comprehensive .NET toolkit for AI agent evaluation featuring fluent assertions, stochastic testing, model comparison, and security evaluation built specifically for Microsoft Agent Framework
Voice Agents
Open-source Docker-based development environment specifically designed for LangChain AI agent experimentation, featuring QuestDB time-series database, Grafana visualization, Code-Server web IDE, and Claude Code integration for autonomous agentic development workflows
Voice Agents
AI-powered contact center platform with power dialer, business SMS, AI voice agents, and CRM integrations for sales and support teams.
Voice Agents
Build, deploy, and manage autonomous AI agents that use foundation models to automate complex tasks, analyze data, call APIs, and query knowledge bases — all within the AWS ecosystem with enterprise-grade security.
💡 Pro tip: Most tools offer free trials or free tiers. Test 2-3 options side-by-side to see which fits your workflow best.
A typical voice stack runs three sequential models: speech-to-text, an LLM, then text-to-speech. Each hop adds latency and the STT step throws away tone, pacing, and emotion. Ultravox uses a single speech-native model that takes audio in and produces a conversational response directly, which both reduces end-to-end latency to sub-second levels and preserves paralinguistic signals the model can reason about.
Yes. Ultravox is designed to plug into telephony providers such as Twilio so you can build inbound and outbound phone agents, and it also supports WebRTC for browser- and app-based voice. You bring the telephony account; Ultravox handles the real-time voice intelligence.
Yes. Voice agents built on Ultravox can call developer-defined tools and functions during a live conversation, which means they can look up records, hit internal APIs, transfer calls, send messages, or trigger workflows — not just chat.
The Ultravox model has been published on Hugging Face and can be self-hosted, which is unusual in the real-time voice AI space. Most teams still use the managed API for production because it handles scaling, infrastructure, and telephony integration, but the open weights are available for teams that need full control.
Fixie.ai is the company's previous name and broader agent-platform identity. The team focused down on real-time voice and rebranded to Ultravox, which is now both the product and the underlying speech-native model. Existing Fixie API users were migrated onto the Ultravox platform.
Compare features, test the interface, and see if it fits your workflow.