U.S. AI Startups Keep Mega-Rounds Rolling in 2025

2025 is shaping up as an encore to 2024’s blockbuster year for AI fundraising. With only a few weeks left in Q3, U.S. startups have already matched last year’s appetite for mega-rounds: multiple $100 million plus financings and several billion-dollar infusions have flowed into labs, healthcare platforms, developer tooling, and AI infrastructure companies.

What happened so far in 2025

The year features landmark raises across multiple categories. OpenAI closed an unprecedented $40 billion round in March, Anthropic raised $3.5 billion, and new research labs like Thinking Machines Lab secured massive seed funding. Healthcare-focused startups such as Abridge and Ambience Healthcare pulled in hundreds of millions, while infrastructure and tooling companies — from model-benchmarks to GPU-hardware firms — continued to attract large rounds.

• OpenAI: $40B round valuing the company at $300B.
• Anthropic: $3.5B Series E at a $61.5B valuation.
• Thinking Machines Lab: $2B seed round valuing the company at $12B.
• Abridge: $300M Series E, now valued above $5B.
• Glean: $150M Series F at $7.25B valuation.
• Runway, Anysphere, Lambda and others each pulled large rounds that highlight capital flow into creative tools and infrastructure.

What this funding pattern means

Investors are doubling down on compute-heavy model builders, deep research labs, and vertical platforms that pair AI with regulated domains like healthcare and legal. The mix of mega-seed, Series C–E, and even repeat mega-rounds underlines two dynamics: capital concentration around winners, and high investor conviction that specialized AI products will capture enterprise budgets.

For founders this means tougher competition for headlines but clearer routes to scale if you can demonstrate real-world ROI and regulatory readiness. For VCs and corporate backers, it raises questions about portfolio diversification, valuation risk, and how to support capital-intensive scaling.

What to watch next

Keep an eye on whether funding continues to favor broad model builders or shifts toward niche, regulated applications that can monetize faster. Also watch infrastructure spend — hardware, data labeling, and model evaluation tools — as these layers will determine who can sustainably operate at scale.

At QuarkyByte we parse these flows not as headlines but as signals. We translate valuation trends and investor participation into actionable frameworks for fundraising strategy, go-to-market prioritization, and risk planning — helping startups, enterprise teams, and institutional investors turn capital trends into measurable outcomes.