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Last Energy: A New Chapter for Nuclear Power and a Near Term Path to the Power Bottleneck

WDWI Last Energy (1)

Why We Invested in Last Energy

We are in the early innings of a generational shift in energy. Compute demand is accelerating, driven by hyperscale AI, industrial digitization, and global electrification, while the grid faces hard constraints around speed, reliability, and clean baseload supply.

This week, we published Our Energy Thesis and Do We Have Enough Power?, which distilled a simple conclusion. When you travel all the way down the stack, compute is physical, and power is becoming the pacing constraint for the next decade of AI and data-center growth. We believe energy is the foundational layer beneath many of these sectors, and without a credible path to expanding clean, firm power, progress in all sectors could slow.

That belief led us to invest in Last Energy. Rather than inventing new reactor physics, the company is focused on productizing nuclear power through manufacturability, repeatability, and deployment at scale, with the goal of delivering clean, firm power on timelines that match the build-out of modern compute infrastructure.

Why We Backed the Team

When we first met founder and CEO Bret Kugelmass, it was clear he was building an energy company, not a research program. Bret is an accomplished mechanical engineer with a master’s degree in Robotics from Stanford and a multi-time founder. He previously founded Airphrame, one of the early autonomous drone operators in U.S. airspace. In 2017, Bret founded the Energy Impact Center, where he hosted more than 1,500 discussions with experts on nuclear energy prior to launching Last Energy.

He’s assembled a team with depth across engineering, operations, and regulatory execution, built to move quickly while operating within nuclear’s stringent safety and licensing requirements.

The Product Behind the Vision

At the center of Last Energy’s strategy is its proprietary 20 MWe microreactor (PWR-20), designed around tested pressurized water reactor (PWR) technology. Last Energy integrates primary systems into a single, hermetic steel containment. This design innovation replaces complex nuclear-grade systems with engineered steel, enabling factory manufacturing using commercially available supply chains. A TechCrunch article on December 16th outlines “What sets Last Energy apart from competitors is its approach: The company is using an old reactor design developed by the government decades ago.” Furthermore, the startup’s reactor is not designed to be serviced over its operating life. Instead, each reactor core is permanently sealed inside roughly 1,000 tons of steel, creating a fully self-contained unit.

Microreactor Last Energy 1

Image of microreactor provided by Last Energy

Once commissioned, the sealed nuclear island operates like a battery and runs for six years without the need for refueling or on-site maintenance. Other than the required electrical and control interfaces, there are no penetrations through the steel enclosure, reducing complexity and limiting points of failure over the reactor’s lifetime.

Progress on the Ground

Last Energy is advancing in parallel across regulatory pathways and concrete project execution. In the United States, the company was selected for the Department of Energy (DOE) Reactor Pilot Program and is advancing a pilot effort at Texas A&M’s RELLIS Campus, supporting an anticipated 2026 criticality demonstration. TechCrunch reports the pilot as a 5 MW reactor at the same site. In the United Kingdom, Last Energy has completed a Preliminary Design Review and states it has a regulator confirmed pathway toward a potential 2027 site license decision.

The Series C & Why We Leaned In

On December 16, 2025, Last Energy announced it had closed an oversubscribed Series C of more than $100M that we were a part of, led by the Astera Institute with participation from JAM Fund, Gigafund, The Haskell Company, AE Ventures, Ultranative, and Woori Technology Co., Ltd., among others. Last Energy described the financing as capital that will support the pilot effort and position the business to transition into commercialization, with factory fabrication central to the scale up.

Why This Complements Our Energy Thesis

In our thesis post, we argued that the hard part is not just generating more electrons in aggregate. One of the hard parts is delivering reliable, always-on power to specific strategic locations and industrial clusters quickly enough to match compute deployment.

Last Energy is designed with nearer term reality in mind. It is focused on proven reactor fundamentals paired with innovation in reactor packaging and go-to-market execution. The objective is to make nuclear power easier to deploy repeatedly, closer to load, and in increments that map to how the digital world actually expands.

A Unique Approach

What drew us to Last Energy is their nuanced understanding of the field and regulatory pathways to commercialization. While much of the advanced reactor ecosystem remains research and development heavy, Last Energy is focused on taking known technology and engineering it into a deployable product. The company is seeking to optimize for throughput manufacturing and repeatable delivery.

Equally important is the delivery model. Last Energy markets a full-service approach for customers, including data centers, built around long-term agreements rather than asking customers to become nuclear operators.

Why Now

As Sam Englebardt said in connection with the Series C announcement, “Ensuring steady access to clean power is critical to enabling the next wave of industrial and economic growth.” We believe Last Energy is well positioned to meet this moment with a pragmatic, capital-efficient pathway to deployment that targets the settings that need firm power most.

Policy tailwinds are also strengthening. In the U.S., the White House and DOE have described a set of four nuclear-focused executive orders (May 23, 2025) aimed at modernizing regulation and accelerating deployment pathways. Internationally, nuclear finance constraints have also begun to shift, including recent developments involving the World Bank’s engagement on nuclear energy.

Looking Forward

Over the next 12 months, the milestones we will be watching most closely align with the company’s stated priorities.

  • Advancing the pilot reactor effort and the 2026 criticality milestone

  • Continuing progress on PWR-20 commercialization

  • Expanding manufacturing capabilities and partner engagement, including strengthening the company’s operational footprint in Texas

  • Sustaining momentum across U.S. and U.K. pathways toward initial commercial deployments

The conclusion from our energy thesis is straightforward. If compute is the new industrial base, then firm power is the bottleneck, and Last Energy is building one of the most deployable, commercially oriented paths to relieve it on relevant timelines, in our view.

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