Investors have been flocking to Y Combinator’s Demo Days for years to get their hands on promising startups building cool tech. After all, the accelerator has produced some of the biggest tech companies in the world, from Airbnb and Reddit to Dropbox, Zapier and Stripe.
That’s why we make sure to follow the event to spot the most interesting companies from each batch. As I’ve done nearly every quarter now that the accelerator has moved to four cohorts a year, I asked nearly a dozen investors which startups were most in demand at Y Combinator’s Winter 2026 Demo Day earlier this week.
To ensure that our list included truly sought-after executives, a company had to be marked as a “favorite” by at least two different venture capitalists to make the cut.
When it comes to valuations, I hear at least two startups have raised capital with a $100 million price tag, though mostly those startups are already generating revenue at a run rate of $1 million or more. Even for the less crowded startups not on this list, the “default” valuation this quarter seems to be around $30 million, which investors told me is about double the current seed market average.
Without further ado, here is the list:
Beyond Reach Labs
What it builds: Deployable solar arrays for satellites.
Why it’s a favorite: The startup claims to have developed solar arrays that are the size of a table at launch, but unfold to the size of a football field once in orbit. The founders say their system can increase available power tenfold while reducing costs by 88%. Beyond Reach already has a flight planned for 2027 and says it has secured $325 million in letters of intent from leading space companies.
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Byteport
What it builds: A ridiculously fast file transfer protocol.
Why it’s a favorite: According to Byteport founder Jayram Palamadai, existing file transfer protocols like TCP are too slow for the age of artificial intelligence. That’s why he created DART, short for Dynamic Accelerated Record Transfer, which apparently can transfer large files an average of 10 times faster than TCP and even up to 1,500 times faster over “reliable connections.”
Hex Security
What it builds: Continuous security testing tools with artificial intelligence.
Why it’s a favorite: To combat hackers who use AI to launch unstoppable cyber attacks, Hex builds AI agents that can act as penetration testers, constantly probing for vulnerabilities and security holes in companies’ infrastructure. By automating what was once a manual process that was rarely performed, Hex claims it can prevent attacks at a fraction of the cost. The startup claims to have surpassed run-rate revenue of more than $1 million in just eight weeks, which is perhaps why VC investors, as one person told me, “fought” to invest in the company.
Grazemate
What it builds: Autonomous drones for herd and cattle monitoring.
Why it’s a favorite: Moving cattle across vast ranches is an expensive and dangerous undertaking, often involving helicopters and motorbikes. GrazeMate’s founder, who grew up on a 6,000-head cattle station in Australia, saw a way to make life easier for ranchers, so he dropped out of college to pursue a degree in robotics.
GrazeMate drones can automatically guide cattle to different areas of a ranch, estimate animal weight, grass availability and growth, and can follow pre-defined route plans.
GRU Space
What it builds: Permanent lunar infrastructure, starting with a hotel on the Moon.
Why it’s a favorite: “Humanity will become interplanetary. It’s not a matter of if, but when, and the time is now,” says GRU Space founder Skyler Chan, a recent Berkeley graduate who previously built software at Tesla and worked on NASA-funded space technology.
Chan claims his startup has developed a “moon factory” that can turn lunar soil into building bricks, which he plans to use to build a luxury hotel on the moon as a “wedge” for wider lunar infrastructure. GRU’s astronomical ambitions, including its goal to open the first lunar hotel by 2032, have made it one of the most talked-about startups of this YC batch. The company has already secured $500 million in letters of intent, an invitation to the White House and even a reservation from the Trump family.
Luel
What it builds: A marketplace for human-collected data to train multimodal artificial intelligence.
Why it’s a favorite: Founded by two UC Berkeley dropouts, Luel is building a data marketplace that connects AI model makers with contributors who can submit “everyday life” activities like ironing or patient-doctor conversations to provide audio, video and image data. The company claims to generate nearly $2 million in ARR within six weeks, fueled by high demand from robotics and voice AI labs.
Pax Historia
What it builds: An AI powered alternate history strategy game.
Why it’s a favorite: Pax Historia allows users to rewrite history in a way that traditional strategy games cannot. Using genetic artificial intelligence, the game responds to infinite, complex geopolitical scenarios, from “What if Rome never fell?” in “What if the US occupied Greenland?” The founders claim that the game currently attracts 35,000 daily users who have played nearly 20 million rounds.
Stilta
What it builds: Agentic AI for Intellectual Property and Patent Attorneys.
Why it’s a favorite: Stilta’s founders claim that patent disputes can cost up to $4 million per case, largely due to the cost of manually reviewing documents. The startup says its AI agent can search and analyze patents in databases and scientific literature, saving time and legal fees.
The company’s agents are already used by IP lawyers at pharmaceutical giant Roche. For investors, another attractive aspect is that the founders are from Sweden — recent Swedish successes like Lovable and Legora have created something of a “halo” around companies from the region, one VC investor said.
