Ultravox vs Sim
A detailed comparison to help you choose between Ultravox and Sim.
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Verdict: Sim wins
Sim scores 3.9/5, edging out Ultravox at 3.8/5. Technical teams that want an inspectable, self-hostable agent orchestration layer with real governance controls instead of a closed agent builder.
Ultravox Real-time, speech-native voice AI | Sim Build and test AI agents without code | |
|---|---|---|
| Rating | 3.8 (1 review) | 3.9 (1 review) |
| Pricing Model | paid | freemium |
| Starting Price | From $49/mo | Free tier available |
| Best For | Engineering teams building latency-sensitive voice agents who want a speech-native conversation layer with clean APIs rather than a stitched cascade. | Technical teams that want an inspectable, self-hostable agent orchestration layer with real governance controls instead of a closed agent builder. |
| Free Tier | ||
| API Access | ||
| Team Features | ||
| Open Source | ||
| Tags | team featuresapi access | open sourcefree tierapi access |
| Visit Ultravox → | Visit Sim → |
Ultravox
Pros
- + Speech-native model handled interruptions and overlaps without the cascade failure I have seen in STT/LLM/TTS stacks
- + Mid-call tool execution in my test paused and resumed speech without dead-air gaps
- + Transparent metered pricing: 30 free minutes then $0.05/min, verified by third-party price tracking in August 2026
- + Open model weights (fixie-ai/ultravox) allow self-hosting for teams that need model-level control
- + RAG corpora and custom voices are configuration steps, not build steps
Cons
- - Acquired by Inworld AI on 1 October 2026 — continuity is promised but the roadmap is unwritten
- - No free plan beyond the 30-minute allowance; sustained experimentation is paid
- - Developer-only product: no visual agent studio, no templates for non-engineers
- - Pay-as-you-go caps at 5 concurrent calls, which queued my parallel test calls
- - The hosted platform (scheduler, telephony, voice management) is where the value sits, so open weights are not a free substitute
Sim
Pros
- + Per-block run traces show inputs, outputs, duration and cost for every step — in my 50-run test this made the two retry-plagued runs immediately visible
- + Apache-2.0 codebase self-hosted via Docker Compose in about fifteen minutes in my test, with the same canvas and logs as the hosted workspace
- + Typed workflow vocabulary (Router, Guardrails, Evaluator, Human-in-the-Loop) forces you to say where decisions and quality checks happen
- + Free tier with 1,000 credits, plus per-member spend limits and permission groups for model and integration access
- + Deploys as chat, API or MCP server from the same workflow
Cons
- - Plan details churned through 2026: third-party trackers disagree on whether the free 1,000 credits are monthly or one-time
- - Integration count claims conflict — the homepage says 270+, directory listings say 1,000+
- - Governance stack (SSO, SOC 2, audit logs, self-hosting support) is gated at Enterprise pricing
- - Product launched publicly in 2025 and is still moving under users; no native mobile app
- - Support is a community repository below Enterprise
Frequently Asked Questions
Which is better, Ultravox or Sim?▼
Sim scores higher at 3.9/5 vs 3.8/5 for Ultravox, making it the better-rated option in our comparison.
What is the difference between Ultravox and Sim?▼
Ultravox: Ultravox, formerly Fixie, is a real-time voice AI infrastructure layer for building fast, natural-sounding voice agents. Sim: Sim is an open-source AI workspace where companies build, distribute and govern AI agents, with hundreds of integrations, all major LLMs and a self-hosting option.
Is Ultravox or Sim more affordable?▼
Ultravox starts at €49/mo, Sim starts at €0/mo. Check the comparison table above for current pricing.
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