Delphi saved 10 months of engineering work with Vapi
Overview
Delphi.ai is a digital cloning platform that enables creators, coaches, and experts to create custom LLM’s of themselves, allowing them to scale their expertise and availability across multiple channels 24/7.
When Delphi’s founders saw that voice calling was becoming a cornerstone for high‑profile clients such as Arnold Schwarzenegger, HubSpot CEO Brian Halligan, and relationship expert Matthew Hussey, they set out to find infrastructure that could deliver authentic, real‑time conversations at scale.
After struggling with a custom WebSocket-based voice solution, Delphi chose Vapi for its reliability, speed, and ability to handle the “difficult dance” of delivering highest-quality responses in near-real time.
This allowed them to focus on their core competitive advantage: building the best digital minds.
"At first I was like, I’ll do it myself.. but eventually I realized: What’s our competitive advantage? It’s not voice-calling infrastructure; it’s the mind.. So we switched to Vapi."
— Sam Spelsberg, Co-Founder, Delphi
The Challenge
Delphi’s digital minds understand their creators’ knowledge and replicate the way they speak, think, and interact. This required solving a unique technical challenge:
Delivering the highest-quality answer in the shortest possible time while meeting near-real-time expectations.
In traditional telephony, a few seconds of lag is acceptable. In a dynamic, web-based conversation with a digital mind, any perceptible delay breaks the illusion of intelligence.
To achieve this, Delphi built:
- Model context engineering and fine-tuning on top of foundation models
- Custom LLMs (“the brain”) for each creator
- Response delivery in the creator’s authentic voice
But their WebSocket-based voice stack was slow, unreliable, and unscalable. With celebrity clients monetizing through live calls, reliability wasn’t negotiable.
Voice Quality and Provider Switching
The models that power voice AI are improving at an incredible pace. Within the last year, multiple new state-of-the-art TTS models have been released.
For a company like Delphi, where voice quality is paramount, this created a new problem: they needed to constantly integrate the latest and best models to stay competitive, forcing them to rebuild parts of their stack every few months.
The Solution
Why Vapi Won
After a team member tested Vapi and found it outperformed their custom build, Spelsberg made the switch.
This allowed their team to dedicate their time to:
- Fine-tuning custom LLMs for each creator.
- Engineering the context that makes each AI clone authentic.
- Improving the quality of the insights delivered by the "mind."
The most significant metric Delphi saw improve was engineering overhead.
By integrating Vapi, Delphi immediately eliminated the need to have engineers working on the voice-calling stack.
They could trust the infrastructure would work, keeping their team lean and focused on the core product.
"Vapi let us offload that entire layer, keep effort minimal, and still deliver a product whose keystone feature is voice calling."
— Sam Spelsberg, Co-Founder, Delphi
Results
- Engineering Hours Saved: Delphi avoided about 10 months of engineering work required to build, scale, and maintain a production-grade voice infrastructure and was able to launch within 8 weeks with Vapi.
- Rapid scale: Delphi managed to scale from 0 to 100k+ mins in usage in less than 1 month after switching to Vapi.
- Focus on Core Value: The engineering team was freed to work on what makes Delphi unique rather than what doesn't.
- Production-Grade Reliability: By moving to Vapi’s infrastructure, Delphi inherited a platform with 99.99% uptime, eliminating the risk of failure during peak, revenue-generating moments.
- Future-Proof Voice Quality: Vapi’s provider abstraction ensures Delphi customers always benefit from the best available voice engines.
- Confidence in Scaling Beyond Voice: By handling the most complex part of real-time infra today, Vapi has earned Delphi’s trust as they look to solve adjacent bottlenecks like SMS compliance at scale.
Delphi’s impact today:
Delphi is rapidly onboarding celebrities, with Arnold Schwarzenegger, Jay Shetty, Codie Sanchez, and others now running digital minds on the platform.
Creators such as Matthew Hussey have generated millions in recurring revenue through voice-enabled digital minds. The company has also earned strong investor validation, securing a $16M Series A led by Sequoia.
About Vapi
Vapi is the developer-centric Voice AI platform enabling businesses to build, test, and deploy advanced voice assistants with sub-500ms latency, infinite concurrency, and enterprise-grade reliability. With modular, provider-agnostic architecture and powerful APIs, Vapi lets customers integrate best-in-class AI components and go from prototype to production in days.