Startup developers of fusion energy—the so-called power of the stars in a jar—are racing to prove their technologies and bring clean, limitless electricity to the grid to meet the power needs of the AI boom. While Helion has the most aggressive timeline for first commercial power—under contract for Microsoft data centers—skeptics have questioned Helion’s start date; its unique technological approach versus competitors; and its relative lack of scientific updates until now.

“While interstitial milestones are really important to show that the technology works and you can get regulatory approval, at the end of the day, it’s about deploying power plants at scale to support the growing power needs,” Helion cofounder and CEO David Kirtley told Fortune.

“We’re on schedule to still have first electrons to the grid in 2028. It is an aggressive milestone. It’s going to be hard,” Kirtley said. “Part of that is the progressive iteration and parallel development right now in Malaga, Washington.”

While the plasma heat achievement was set at Helion’s seventh-generation prototype, Polaris, in suburban Seattle, Helion already is building its 50-megawatt commercial power plant, Orion, 130 miles away in Malaga—near Microsoft’s growing data center campus. Helion is not yet assembling the fusion reactor, which requires additional engineering and design fine-tuning.

Developing multiple projects in parallel—including an assembly line manufacturing system—is key to Helion’s rapid pace and success, Kirtley said. “It’s how we have been able to build seven generations of fusion systems and do it much quicker than anyone else in fusion. Core to the philosophy of how we operate is that rapid build, test, iterate, and build again.”

Whereas traditional nuclear fission energy creates power by splitting atoms, fusion uses heat to create energy by melding them together. In the simplest form, it fuses hydrogen found in water into an extremely hot, electrically charged state known as plasma to create helium—the same process that powers the sun. When executed properly, the process triggers endless reactions to make energy for electricity. But stars rely on overwhelming gravitational pressure to force their fusion. Here on Earth, creating and containing the pressure needed to force the reaction in a consistent, controlled way remains an engineering challenge.

And because fusion reactors are so much smaller than stars, they need to produce heat in much hotter concentrations. The sun is about 15 million degrees Celsius at its core, or 27 million degrees Fahrenheit.

About 100 million degrees Celsius is considered the minimum threshold for sustained commercial fusion power, hence the enthusiasm over the new milestone.

Helion was founded in 2013, and Altman became chairman and a major financial backer in 2015—shortly before he cofounded OpenAI. Altman also became chair of the nuclear fission, small modular reactor (SMR) startup Oklo that same year. Other key Helion investors include LinkedIn cofounder Reid Hoffman and Facebook cofounder and current Asana CEO Dustin Moskovitz. Kirtley said Altman’s role is to focus on the long-term vision.

“A question I get from Sam is, ‘How do we move faster?’” Kirtley said. “We’re already on an aggressive time frame. ‘How do we move faster than that? How do we deploy power at scale quickly?’”

Unique fusion approach

Kirtley previously worked at NASA-backed MSNW on fusion-driven rocket technologies. He cofounded Helion with a dual focus of fusion power and fusion propulsion. The propulsion work helped Helion innovate its unique power approach, he said.

“One thing you learn about working in space and building systems to fly in space is you can’t waste anything. Every ounce of weight is critical; every watt of power is critical,” Kirtley said. “You must be very efficient everywhere and all the time. If you take that same approach and apply it to fusion, all the physics requirements dramatically reduce.”

Most fusion technologies, as well as nuclear fission, are based on generating heat to power steam turbines, which produce the electricity. Helion’s technology captures the electricity during the fusion process—skipping the need for turbines.

“That’s really the fundamental difference that we believe allows us to move much faster than other people,” Kirtley said. “That shrinks the scale of the fusion system. It minimizes how hard it is to do.”

Helion’s fusion fuel combines deuterium from water with tritium. Helion was the first company licensed to use radioactive tritium as a fusion source. But the end goal is to use deuterium and helium-3, which Helion aims to produce by fusing the same deuterium atoms. Helium-3 allows the process to generate more electricity with less heat.

Arguably Helion’s chief fusion competition is Nvidia and Bill Gates–backed Commonwealth Fusion Systems (CFS), which has deeper pockets but is taking a more conservative approach. Commonwealth leans on the most traditional fusion technology—highly relative for a nascent industry that’s never generated electricity on the grid.

CFS is currently building its SPARC fusion prototype to come online next year. But that won’t provide power to the grid. If SPARC succeeds, CFS’s first commercial fusion plant, ARC, is slated to be built and to come online in the early 2030s just outside of Richmond, Va. If all goes as planned, the 400-megawatt plant—much more power than Helion’s Orion—would produce enough electricity to service about 300,000 homes.

CFS leans on the so-called tokamak design—shortened from toroidal magnetic chamber—which relies on its powerful magnets. The technology essentially involves a massive, doughnut-shaped machine that traps the plasma in a high-temperature, superconducting magnetic field. But the process generates heat, not electricity.

Helion’s smaller, but faster approach uses magneto-inertial fusion. Theoretically, the plasmas collide in the fusion chamber and are compressed by magnets around the machine. That heats the plasma, initiating fusion reactions and resulting in a change in the plasma’s magnetic field. This change interacts with the magnets, increasing their magnetic field, and initiating a flow of new electricity through the coils.

The bottom line is it’s quite complicated, and there’s no guarantee of success for any of the fusion developers. But Kirtley said he’s confident fusion power can make a notable dent in the U.S. power grid within the next decade and keep growing from there.

“If all we do is build the world’s first fusion power plant, as a company, we failed,” Kirtley said. “Our goal is to deploy clean and safe baseload power to the world. That means building technologies in a way that is scalable, mass producible, and must be low cost so that the customer wants it.”