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In almost every way, Leo Paz is following a well-worn path to Silicon Valley success. The 27-year-old Canadian earned a degree in software engineering, co-founded a startup that was accepted into the vaunted Y Combinator accelerator program, and moved to San Francisco to build it.
But in another way, he’s unlike any of his predecessors: Since landing in the world capital of software development, he’s let AI do all the coding. Paz has been spending 14-hour days instructing large language models to do the work for him, “vibe coding” his sales agent startup Outlit all the way to Y Combinator demo day in April.
“I don’t think YC knew exactly how much code was being written by LLMs,” he told Semafor. It found out earlier this year after a founder survey. “They were kinda shocked,” he added.
While vibe coding has helped people without any technical experience create software through AI-powered assistants, the practice is also sweeping the upper echelons of the startup ecosystem, where, until recently, software talent was the scarcest and most coveted resource. The change is shifting the balance of power from the most talented coders to anyone who has a great idea, opening the door to Silicon Valley’s next generation of unicorns.
In March, Y Combinator CEO Garry Tan said 25% of startups in that winter’s class generated 95% of their code using AI tools. The numbers are likely to be much higher in the next batch, which culminates with a demo day this month.
Founders of startup Mastra, which developed a JavaScript framework for building agents, held weekly vibe coding whiteboard sessions in their San Francisco apartment with other startups in their YC cohort. Fueled by takeout from Gai Chicken & Rice, founders would gather under a projector light to learn the ins and outs from the Mastra team.
Chief Technology Officer Abhi Aiyer said his full-time job is prompting the AI on what to build. “All of us know what we’re doing, so we don’t actually write code that much,” he said of the startup team. “I just think and review” the code written by AI, he added.
Jackson Stokes of model reinforcement startup TrainLoop, also in that YC class, said he has been vibe coding his product’s user interface. “It definitely changes our calculus on potentially hiring a designer,” he said. “I don’t know if it’ll ever come back into scope, to be honest.”
Outside of YC, Pukar Hamal, CEO of SecurityPal — which helps companies automate responses to security-related questions during the sales process — is vibe coding agents to fill some open positions rather than hiring personnel.
SecurityPal needed a product manager, and instead of creating a job posting, Hamal spent three hours vibe coding an agent named Penelope, depicted as a brunette mountaineer wearing aviator goggles and a fur-lined bomber jacket (a nod to the company’s office in Nepal). “Penelope is going to be a very integral part of how I as a CEO make decisions,” he told Semafor. “She’s also going to be part of my leadership meetings, where we can interrogate her on different ideas we have.”
SecurityPal has incorporated two vibe-coded agents into the security analyst team, which manages security data sharing between customers. The company onboarded them like it would any employee, and they participate in all-hands meetings — camera on. “We’ve probably already hired our last security analyst,” he said.
