
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
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:
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.
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:
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

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.
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.