AI startups announced 410 Series B rounds from January to September 2026, about as many as the 421 in the same months of 2025. The rounds got bigger. The median Series B with a disclosed size was $46M, up from $40M a year earlier and $31M in 2024.
The change is sharpest at the top. 94 AI Series B rounds reached $100M or more, against 39 in the first nine months of 2025. 25 reached $250M, against 6. Those 25 are listed below, from Prometheus’s $12B round in June to four $250M rounds.
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The 25 largest AI Series B rounds of 2026
Every round of $250M or more announced as a Series B from January 1 to September 30, 2026, ranked by size. Rounds of equal size are listed by announcement date. Amounts in other currencies are converted to US dollars at one rate per currency. Valuations are as reported at the time of the round, generally post-money.
| # | Company | What it does | Country | Announced | Amount | Led by | Valuation |
|---|---|---|---|---|---|---|---|
| 1 | Prometheus | AI for engineering and manufacturing design | United States | Jun 2026 | $12B | Not disclosed | About $41B |
| 2 | Isomorphic Labs | AI drug design | United Kingdom | May 2026 | $2.1B | Thrive Capital | Not disclosed |
| 3 | Valar Atomics | Small nuclear reactors to power AI data centers | United States | Aug 2026 | $1B | Sequoia Capital | $6B |
| 4 | MatX | Chips for training and running large language models | United States | Feb 2026 | $500M | Jane Street, Situational Awareness | Not disclosed |
| 5 | Nexthop AI | Network switches for AI data centers | United States | Mar 2026 | $500M | Lightspeed Venture Partners | $4.2B |
| 6 | CuspAI | AI for discovering new materials | United Kingdom | Jul 2026 | $450M | Kleiner Perkins, NEA | $2.6B |
| 7 | Tripo | 3D models from text and images | China | Sep 2026 | RMB 3B (about $448M), Series B and B+ | Not disclosed | Not disclosed |
| 8 | Meshy | 3D models from text and images | United States | Jul 2026 | $400M | Not disclosed | $1.5B |
| 9 | Higgsfield | AI video generation | United States | Aug 2026 | $400M | DST Global | $5.4B |
| 10 | TensorWave | AI cloud built on AMD GPUs | United States | Jun 2026 | $350M | Magnetar, AMD Ventures | $1.55B |
| 11 | Odyssey | World models that simulate the physical world | United States | Jun 2026 | $310M | Natural Capital | $1.45B |
| 12 | Mariana Minerals | Software-run critical minerals projects | United States | Aug 2026 | $310M | Khosla Ventures | $1.5B |
| 13 | OLIX | AI inference chips | United Kingdom | Aug 2026 | €270.5M (about $303M) | Not disclosed | €2.8B |
| 14 | Amca | AI-driven manufacturing of aerospace and defense parts | United States | May 2026 | $300M | Caffeinated Capital | More than $1B |
| 15 | Gimlet Labs | Software that runs AI inference across different chips | United States | Sep 2026 | $300M | Andreessen Horowitz | $3B |
| 16 | SiliconFlow | AI inference cloud | China | Jun 2026 | More than RMB 2B (about $299M) | Not disclosed | Not disclosed |
| 17 | ShengShu | Vidu AI video generator | China | Apr 2026 | RMB 2B (about $299M) | Alibaba Cloud | Not disclosed |
| 18 | X Square Robot | AI models and robots for general physical tasks | China | Apr 2026 | Nearly RMB 2B (under $299M) | Xiaomi, HongShan | Not disclosed |
| 19 | Wispr | Voice dictation app | United States | Aug 2026 | $280M | Menlo Ventures | $2B |
| 20 | Cowboy Space Corporation | Orbital data centers and launch vehicles | United States | May 2026 | $275M | Index Ventures | $2B |
| 21 | Bedrock Robotics | Autonomy kits for construction machines | United States | Feb 2026 | $270M | CapitalG, Valor Atreides AI Fund | $1.75B |
| 22 | Mirador Therapeutics | Immunology and fibrosis drugs, found with machine learning on patient data | United States | Jan 2026 | $250M | Not disclosed | Not disclosed |
| 23 | Upwind | Cloud security | United States | Jan 2026 | $250M | Bessemer Venture Partners | $1.5B |
| 24 | TENEX.AI | AI-based threat detection and response | United States | Mar 2026 | $250M | Crosspoint Capital Partners | Not disclosed |
| 25 | Instinct | AI assistant reached by phone or text | United States | Aug 2026 | $250M | Index Ventures, Benchmark | $2.5B |
Tripo announced its Series B and Series B+ together, so the amount covers both. Instinct’s round was reported in August and has not been announced by the company. Mirador Therapeutics announced its Series B in January 2026 after closing it in the third quarter of 2025.
Eighteen of the 25 are US companies. China has four (Tripo, SiliconFlow, ShengShu and X Square Robot) and the UK has three (Isomorphic Labs, CuspAI and OLIX).
Compute and chips took the most big checks
Eight of the 25 build or power the infrastructure behind AI. MatX and OLIX design AI chips. Nexthop AI makes the network switches that connect GPUs. TensorWave and SiliconFlow rent out computing power for training and running models, Gimlet Labs splits AI workloads across different chips, and Cowboy Space Corporation is building data centers in orbit. And Valar Atomics’ $1B, led by Sequoia Capital at a reported $6B valuation, pays for small nuclear reactors meant to power AI data centers. More on this layer is in our list of top AI infrastructure startups.
Nexthop AI’s $500M valued the company at $4.2B. It was founded in 2024 by Anshul Sadana, a former Arista executive.
Science, robots and creative tools
Isomorphic Labs, the drug design company that came out of Google DeepMind, raised the largest Series B after Prometheus: $2.1B led by Thrive Capital, after a first outside round of $600M in 2025. CuspAI raised $450M for AI-driven materials discovery, and Mirador Therapeutics raised $250M for immunology drugs.
Prometheus, which Jeff Bezos runs as one of its two co-CEOs, is building AI to design and manufacture physical products. Its $12B Series B at about $41B came seven months after it launched with a round of more than $6B.
Robotics and physical-world AI took four places: Odyssey’s world models, X Square Robot’s general-purpose robots, Bedrock Robotics’ kits that let excavators run on their own, and Amca’s AI-driven parts factories.
Creative tools took four more. Tripo and Meshy turn text and images into 3D models, Higgsfield makes AI video for creators and brands, and ShengShu makes the Vidu video generator. Higgsfield’s $400M Series B, led by DST Global, valued it at $5.4B, about four times its valuation in January.
The share of $100M Series B rounds more than doubled
Of the 400 AI Series B rounds with a disclosed size in the first nine months of 2026, 94 were $100M or more, or 23.5%. In the same months of 2025 that share was 9.6%. Rounds under $50M fell from 64% of disclosed Series B rounds to 51%.
The median rose through the year: $42M in the first quarter, $48.1M in the second and $50M in the third. The number of rounds slipped from 150 in the first quarter to 136 and then 124 in the third.
AI Series B rounds raised $44.0B in total. Without Prometheus, the figure is $32.0B, against $22.8B in the first nine months of 2025. For how the same pattern looks across all stages, see our breakdown of the largest rounds in AI mega-rounds of 2026.
Where AI Series B money goes, by sector
By number of rounds, developer tools and AI infrastructure led with 73, followed by manufacturing and industrials with 70 and health and biotech with 54. Fintech had 41 and energy 34. Many companies fit two sectors, so these counts add up to more than the 400 rounds.
The US leads on count and round size
US companies raised 225 of the 400 AI Series B rounds with a disclosed size, 56%, at a median of $55M. India had the second most, 37, but at a median of $18M. The UK had 27 at a median of $41M. China had 21, and its median of $144M was the highest among the eight countries with the most rounds. Our US AI funding report for the first half of 2026 and Europe AI funding report cover each region in more detail.
How we count
The list and figures cover AI startup rounds announced as Series B from January 1 to September 30, 2026, with the same months of 2024 and 2025 for comparison. Series B extensions, Series B-1 and B-2 tranches and pre-Series B rounds are not counted, except Tripo’s Series B and B+, which were announced as one raise. Amounts are as announced and converted to US dollars; medians use rounds with a disclosed size. Stage names are explained in our AI startup glossary and AI startups by funding stage.
Seven 2026 rounds that are sometimes listed as Series B are not counted: Neysa’s Blackstone-led raise in India ($600M of equity plus planned debt, with no series label), Valar Atomics’ April raise (about $450M including $110M of debt, unlabeled), Mind Robotics’ $400M (the company’s announcement names no series), Genspark’s $385M (an extension of its existing Series B), Cloaked’s $375M (Series B equity combined with growth financing in an undisclosed split), Spirit AI’s roughly $290M (two back-to-back rounds) and Ollin Biosciences’ $330M (an eye drug developer without an AI product).
Frequently asked questions
What is a Series B round for an AI startup?
A Series B is usually a company’s second priced equity round after its Series A, raised once it has a working product and paying customers. For AI startups in 2026 the median Series B was $46M, and 25 rounds reached $250M or more.
How big is a typical AI Series B round in 2026?
The median AI Series B with a disclosed size was $46M from January to September 2026, up from $40M in the same months of 2025 and $31M in 2024. About one in four, 94 of 400, raised $100M or more.
What was the largest AI Series B round of 2026?
Prometheus, the AI engineering company where Jeff Bezos is co-CEO, raised $12B in a Series B in June 2026 at a valuation of about $41B. The next largest was Isomorphic Labs’ $2.1B in May, led by Thrive Capital.
Which AI startups raised Series B rounds of $500M or more in 2026?
Five: Prometheus ($12B), Isomorphic Labs ($2.1B), Valar Atomics ($1B), MatX ($500M) and Nexthop AI ($500M), all announced between February and August 2026.
How many AI Series B rounds were there in 2026?
410 from January to September 2026, against 421 in the same months of 2025 and 391 in 2024. The count held steady while round sizes grew.
Which country has the most AI Series B rounds?
The US, with 225 of the 400 AI Series B rounds that disclosed a size from January to September 2026, at a median of $55M. India had 37, the UK 27 and China 21.
About the author
Editorial Staff
The Editorial Staff at Bot Memo is a team of writers, analysts, and AI agents dedicated to mapping the global AI startup ecosystem. Led by Chintan Zalani, the team tracks thousands of funding rounds, classifies companies across verticals, and distills it all into actionable intelligence for investors and founders.
