• Speech-native model processes audio directly, eliminating STT→LLM→TTS pipeline latency and producing sub-second response times that feel conversational rather than transactional.
• Preserves paralinguistic information (tone, pace, hesitation) that traditional cascaded pipelines discard, leading to more natural turn-taking and barge-in handling.
• Open-source Ultravox model published on Hugging Face gives teams the option to self-host for cost, latency, or compliance reasons instead of being locked into a proprietary API.
• First-class integration path with telephony providers like Twilio plus WebRTC support, making it practical to ship real phone-call agents and in-app voice without building media plumbing from scratch.
• Tool/function calling is supported inside live voice sessions, so agents can take real actions (lookups, transfers, bookings, CRM writes) rather than only chatting.
• Developer-first surface area: API, JavaScript SDK, and clear primitives for building agents, which suits engineering teams already comfortable with LLM tooling.

⚠️ Consider This

• Pure developer platform with no visual builder or no-code flow designer, so non-engineers cannot stand up an agent without writing code.
• Voice and language coverage is narrower than long-established TTS/STT vendors that have spent years accumulating locales, accents, and voice libraries.
• Speech-native architecture is newer than the cascaded STT+LLM+TTS approach, so tuning, debugging, and observability tooling around it is less mature than the pipeline ecosystem.
• Costs at scale can be hard to predict for high-volume telephony workloads because pricing combines model usage with telephony minutes from third-party providers.
• Branding/identity churn (Fixie.ai → Ultravox) means older documentation, blog posts, and integration guides on the public web can be inconsistent or outdated.

What Users Say About Ultravox (formerly Fixie.ai)

👍 What Users Love

✓Speech-native model processes audio directly, eliminating STT→LLM→TTS pipeline latency and producing sub-second response times that feel conversational rather than transactional.
✓Preserves paralinguistic information (tone, pace, hesitation) that traditional cascaded pipelines discard, leading to more natural turn-taking and barge-in handling.
✓Open-source Ultravox model published on Hugging Face gives teams the option to self-host for cost, latency, or compliance reasons instead of being locked into a proprietary API.
✓First-class integration path with telephony providers like Twilio plus WebRTC support, making it practical to ship real phone-call agents and in-app voice without building media plumbing from scratch.
✓Tool/function calling is supported inside live voice sessions, so agents can take real actions (lookups, transfers, bookings, CRM writes) rather than only chatting.
✓Developer-first surface area: API, JavaScript SDK, and clear primitives for building agents, which suits engineering teams already comfortable with LLM tooling.

👎 Common Concerns

⚠Pure developer platform with no visual builder or no-code flow designer, so non-engineers cannot stand up an agent without writing code.
⚠Voice and language coverage is narrower than long-established TTS/STT vendors that have spent years accumulating locales, accents, and voice libraries.
⚠Speech-native architecture is newer than the cascaded STT+LLM+TTS approach, so tuning, debugging, and observability tooling around it is less mature than the pipeline ecosystem.
⚠Costs at scale can be hard to predict for high-volume telephony workloads because pricing combines model usage with telephony minutes from third-party providers.
⚠Branding/identity churn (Fixie.ai → Ultravox) means older documentation, blog posts, and integration guides on the public web can be inconsistent or outdated.

Pricing FAQ

How is Ultravox different from stitching together Whisper, GPT, and ElevenLabs?

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.

Can I use Ultravox for real phone calls?

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.

Does Ultravox support tool calls and function execution?

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.

Is Ultravox open source?

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.

What happened to Fixie.ai?

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.

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Is Ultravox (formerly Fixie.ai) Worth It?

✅ Why Choose Ultravox (formerly Fixie.ai)

• Speech-native model processes audio directly, eliminating STT→LLM→TTS pipeline latency and producing sub-second response times that feel conversational rather than transactional.
• Preserves paralinguistic information (tone, pace, hesitation) that traditional cascaded pipelines discard, leading to more natural turn-taking and barge-in handling.
• Open-source Ultravox model published on Hugging Face gives teams the option to self-host for cost, latency, or compliance reasons instead of being locked into a proprietary API.
• First-class integration path with telephony providers like Twilio plus WebRTC support, making it practical to ship real phone-call agents and in-app voice without building media plumbing from scratch.
• Tool/function calling is supported inside live voice sessions, so agents can take real actions (lookups, transfers, bookings, CRM writes) rather than only chatting.
• Developer-first surface area: API, JavaScript SDK, and clear primitives for building agents, which suits engineering teams already comfortable with LLM tooling.

⚠️ Consider This

• Pure developer platform with no visual builder or no-code flow designer, so non-engineers cannot stand up an agent without writing code.
• Voice and language coverage is narrower than long-established TTS/STT vendors that have spent years accumulating locales, accents, and voice libraries.
• Speech-native architecture is newer than the cascaded STT+LLM+TTS approach, so tuning, debugging, and observability tooling around it is less mature than the pipeline ecosystem.
• Costs at scale can be hard to predict for high-volume telephony workloads because pricing combines model usage with telephony minutes from third-party providers.
• Branding/identity churn (Fixie.ai → Ultravox) means older documentation, blog posts, and integration guides on the public web can be inconsistent or outdated.

What Users Say About Ultravox (formerly Fixie.ai)

👍 What Users Love

✓Speech-native model processes audio directly, eliminating STT→LLM→TTS pipeline latency and producing sub-second response times that feel conversational rather than transactional.
✓Preserves paralinguistic information (tone, pace, hesitation) that traditional cascaded pipelines discard, leading to more natural turn-taking and barge-in handling.
✓Open-source Ultravox model published on Hugging Face gives teams the option to self-host for cost, latency, or compliance reasons instead of being locked into a proprietary API.
✓First-class integration path with telephony providers like Twilio plus WebRTC support, making it practical to ship real phone-call agents and in-app voice without building media plumbing from scratch.
✓Tool/function calling is supported inside live voice sessions, so agents can take real actions (lookups, transfers, bookings, CRM writes) rather than only chatting.
✓Developer-first surface area: API, JavaScript SDK, and clear primitives for building agents, which suits engineering teams already comfortable with LLM tooling.

👎 Common Concerns

⚠Pure developer platform with no visual builder or no-code flow designer, so non-engineers cannot stand up an agent without writing code.
⚠Voice and language coverage is narrower than long-established TTS/STT vendors that have spent years accumulating locales, accents, and voice libraries.
⚠Speech-native architecture is newer than the cascaded STT+LLM+TTS approach, so tuning, debugging, and observability tooling around it is less mature than the pipeline ecosystem.
⚠Costs at scale can be hard to predict for high-volume telephony workloads because pricing combines model usage with telephony minutes from third-party providers.
⚠Branding/identity churn (Fixie.ai → Ultravox) means older documentation, blog posts, and integration guides on the public web can be inconsistent or outdated.

Ultravox (formerly Fixie.ai) Pricing & Plans 2026

Choose Your Plan

Free / Developer

Pay-as-you-go

Enterprise / Self-hosted

Feature Comparison

Is Ultravox (formerly Fixie.ai) Worth It?

✅ Why Choose Ultravox (formerly Fixie.ai)

⚠️ Consider This

What Users Say About Ultravox (formerly Fixie.ai)

👍 What Users Love

👎 Common Concerns

Pricing FAQ

How is Ultravox different from stitching together Whisper, GPT, and ElevenLabs?

Can I use Ultravox for real phone calls?

Does Ultravox support tool calls and function execution?

Is Ultravox open source?

What happened to Fixie.ai?

Ready to Get Started?

More about Ultravox (formerly Fixie.ai)

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Retell AI Pricing

Bland AI Pricing

Ultravox (formerly Fixie.ai) Pricing & Plans 2026

Choose Your Plan

Free / Developer

Pay-as-you-go

Enterprise / Self-hosted

Feature Comparison

Is Ultravox (formerly Fixie.ai) Worth It?

✅ Why Choose Ultravox (formerly Fixie.ai)

⚠️ Consider This

What Users Say About Ultravox (formerly Fixie.ai)

👍 What Users Love

👎 Common Concerns

Pricing FAQ

How is Ultravox different from stitching together Whisper, GPT, and ElevenLabs?

Can I use Ultravox for real phone calls?

Does Ultravox support tool calls and function execution?

Is Ultravox open source?

What happened to Fixie.ai?

Ready to Get Started?

More about Ultravox (formerly Fixie.ai)

Compare Ultravox (formerly Fixie.ai) Pricing with Alternatives

Vapi Pricing

Retell AI Pricing

Bland AI Pricing