"This place would be amazing in San Francisco!" Macadamia co-founders Brecht Pierreux and Abel Van Steenweghen have just spent ten weeks at Y Combinator in Silicon Valley, “the best startup accelerator on earth,” building AI agents for mechanical engineering teams. Yet even fresh off that high, they insist nothing quite matches the magic of Wintercircus.

If there’s one “crime” you could pin on Brecht Pierreux and Abel Van Steenweghen, it’s impatience. And they’ll happily plead guilty. Halfway through our conversation, Abel remarks that AI is finally picking up speed with the new reasoning models, like GPT-5. When we point out that, for most of the world, it’s already been racing ahead for the past two years, he laughs. “I get it, I do. But for us, it’s been clear all along where this was headed. So we’ve just been impatiently waiting for the tech to catch up. ‘Can we already do this today? No? What about this? Still no?! Damn, maybe tomorrow!’ But honestly, that’s what makes being in AI so exciting right now. It’s a rollercoaster—and so far, there’s no end in sight.”

Truth be told, “waiting impatiently” needs to be taken with a pinch of salt. Abel and Brecht only graduated in 2023, and they haven’t stopped moving since. Brecht wrapped up a master’s in mechanical engineering at ETH Zurich, then hopped to Caltech in Pasadena to finish a thesis in space engineering. Abel earned his master’s in computer science at Delft University of Technology—where the two first met—then boarded a plane to California the moment he graduated.

“At uni, I built an AI app, StudySets.AI, to help students study,” Abel says. “It hit ten thousand users, which was all the excuse I needed to head to Silicon Valley and scale it, meet incredible people, and fall head over heels for the whole ecosystem there.” Brecht, meanwhile, went from an internship at NASA to eight months at SpaceX. “A fantastic experience,” he says. “SpaceX is a huge company, but it still feels like a startup. Still, no matter how much fun I had, ultimately, I was part of a team with a fixed set of tasks to execute. I realized pretty fast that I could do more with the skills I have.”

Their own startup, then? The decision was made in a heartbeat—never mind that Brecht was in Texas and Abel was living the nomadic life in Berlin. “We knew the Y Combinator deadline was coming up,” Brecht says. “It’s the best startup accelerator in the world, and something we’d both dreamed of. And by—pun intended—combining our expertise, and with new reasoning models coming close to the intelligence levels of expert mechanical engineers, we saw there were huge untapped opportunities for AI agents in mechanical engineering.”

“A lot was already happening with AI in software engineering,” Abel continues, “but no one was tackling hardware engineering, with integrations for tools like AutoCAD and Ansys CAE. So we built a demo in two days, pitched it to Y Combinator, and they said yes!” Noticing our raised eyebrows, he laughs and clarifies: after sending in their application, the pair spent the next two weeks working like crazy to level it up. “That’s what Y Combinator is really all about,” he adds. “It’s not enough to have a great idea—you have to prove you can push it forward at breakneck speed.”

What came next, at the start of this year, were ten whirlwind weeks in Silicon Valley. There, Brecht and Abel refined their idea—now called Macadamia—while soaking up advice from heavyweights like Brian Armstrong (Coinbase), Brian Chesky (Airbnb), and Greg Brockman (OpenAI). “The latter was my personal favorite,” Abel admits. “But honestly, every single talk at Y Combinator was incredibly inspiring. And once a week, we sat down with the other startups to trade feedback and track each other’s progress—that’s priceless, too. You swap valuable insights, but you also keep each other accountable and motivated! Because if I’ve learned one thing in San Francisco, it’s that most startup founders burn out emotionally long before they burn out financially.”

Back in Belgium, Abel and Brecht are now running Macadamia (YC W25) from the Wintercircus Startup Campus. Their USP? “We’ve built an AI agent that helps engineering companies automate their administrative grind,” Brecht says. “Right now, we’re focused on Quality Assurance and Quality Control—not just because they produce mountains of paperwork, but also because mistakes here can trigger costly delays. AI models are now more than capable of understanding these processes and supporting engineers. But our endgame is a world where engineers can devote all their time to designing and decision-making—while our AI agent takes care of everything else.

The name Macadamia obviously comes from the nut – “the hardest one to crack,” Abel points out. And the two founders realize there’s still work to be done before AI is reliable enough to fully execute their vision, and crack that nut. But they’re convinced it’s within reach—and soon. “I’m absolutely certain we’ll see artificial general intelligence—human-level AI—within two or three years,” Abel says. Which is why, he adds, they need to get back to Silicon Valley as soon as possible. “I’m not saying Europe lacks expertise—in manufacturing, chemistry, and pharmaceuticals, we’re ahead of the US. And there’s already just as much AI know-how here as over there. But no matter how you spin it, Silicon Valley remains the world’s AI epicenter. That’s where the breakthroughs are happening. So yeah, we need to be there—not in three years, but now.

That also means Abel and Brecht are only staying at the Wintercircus Startup Campus temporarily, while they get all their paperwork in order. “Although I can perfectly imagine this remaining our Belgian base,” says Abel. “I’ve been to tech hubs all over—from Finland to Berlin—and I’m genuinely surprised by the vibe here. So many interesting startups, so much happening all the time, and what a phenomenal building! Honestly, if they had something like this in San Francisco—and they don’t—we’d do anything to get in. A building really can make a difference. But other than that,” he grins, “San Francisco isn’t bad either, right?”

We’ll leave that one hanging.