The Q4 2026 reconstitution of the Prime Unicorn Index brings 12 new private companies into the benchmark, led by a group of fast-growing businesses across defense technology, AI infrastructure, enterprise networking, cybersecurity, healthcare, fintech, and space. The additions arrive during a strong year for the broader Index: through October 21, 2026, the Prime Unicorn Index was up 52.43% year to date, with 238 components representing more than $6.0 trillion in total market value.
Castelion Corporation leads the new additions by a wide margin. The defense technology company enters the Index at a valuation of approximately $13.4 billion, making it the largest company added this quarter. Castelion develops affordable, mass-producible hypersonic strike systems, including Blackbeard, its low-cost hypersonic strike missile designed for mass production and rapid fielding.
Its growth accelerated sharply in 2026. In August, Castelion announced a Series C financing that included $800 million in equity financing and $250 million in committed revolving credit financing, valuing the company at $13 billion. The company has also moved the system closer to production through new U.S. Navy orders, including a September production order valued at up to $200 million.
The second largest addition is Gimlet Labs, entering at roughly $3.0 billion. Gimlet is building AI infrastructure focused on high-performance inference, an increasingly important layer of the AI stack as model usage expands and AI agents take on more complex workloads.
Gimlet’s fundraising trajectory has been particularly rapid. The company announced an $80 million Series A in March 2026 and followed it just months later with a $300 million Series B in September. Gimlet said its customer base had tripled by the time of its Series A, while its Series B announcement highlighted growing demand for AI inference capacity.
Meter is the third-largest new component, with an Index valuation of approximately $2.0 billion. The company provides integrated enterprise networking infrastructure spanning internet connectivity, Wi-Fi, switching, security, deployment, and network management. Meter raised $170 million in a Series C financing in June 2025 led by General Catalyst as it expanded its enterprise networking platform.
Explore the full Q4 2026 Reconstitution Report HERE for a detailed look at all 12 new additions, including company profiles, financing history, valuations, preferred stock terms, and performance comparisons.
Beyond the three largest entrants, the Q4 reconstitution also adds Horizon 3 AI, a cybersecurity company focused on autonomous penetration testing. Muon Space also joins the Index, bringing exposure to a space technology company that develops and operates satellite constellations for commercial and national security missions. Other additions span fintech, healthcare, biotechnology, real estate technology, legal AI, and blockchain intelligence.
Companies Exiting the Index
The quarter also includes eight deletions. EquipmentShare.com, Ethos Technologies, and Generate Biomedicines were removed after exceeding 150 public trading days. MaintainX, Dremio, and Dragos exited following acquisitions, while Highspot and Clari were removed after mergers in which they were not the surviving entities.
These changes illustrate an important part of the reconstitution process: the Index evolves not only as new private companies become eligible, but also as existing constituents age, transact, merge, or leave the private-company universe.
The Q4 changes also highlight several themes shaping private markets heading into 2027. Capital continues to flow toward businesses with significant infrastructure requirements and strategic relevance, particularly in defense, AI, networking, cybersecurity, and space. At the same time, the new class extends well beyond infrastructure, with healthcare, fintech, real estate technology, and legal AI also represented.
With 12 additions and eight removals, the Q4 2026 reconstitution refreshes the Prime Unicorn Index with a new group of companies at very different stages of scale, while offering another snapshot of where growth and capital are concentrating across the U.S. private-company market.
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