NeuralStackTemporal Technologies led the week’s largest U.S. startup funding rounds with a $550 million Series E financing that valued the AI infrastructure company at $12.55 billion. Lightspeed, Wellington Management, Goldman Sachs Alternatives and Tiger Global led the investment in the Bellevue, Washington-based company.
Temporal develops an open source platform for building and operating long-running AI agents and other enterprise systems. Its position at the top of the funding list reflects the continued attention on infrastructure designed to support increasingly complex AI workloads.
Impulse Space ranked second with a $308 million Series D extension. The Redondo Beach, California-based company develops space vehicles that move payloads across and between orbits, and the new financing brings its combined round total to $808 million.
Ridgeline took in $250 million in Series E funding, led by founder and chairman Dave Duffield, at a $1.45 billion valuation. The Incline Village, Nevada-based company operates an AI-enabled investment management platform.
Other large rounds also centered on AI and related infrastructure. Cornelis Networks raised $205 million for networking technology aimed at AI and high-performance computing workloads, while Factory announced $200 million at a $5 billion valuation for its enterprise software development tools. Profound raised $180 million at a $1.8 billion valuation for marketing software intended to help users appear more prominently in AI results.
Why this matters
The week’s financing mix shows that AI investment is extending beyond model development into the systems, networking, coding and marketing applications built around AI adoption. The concentration of large rounds in these categories suggests investors are backing the infrastructure and enterprise software needed to make AI agents and other tools useful at scale.
Foundational AI company Arcee AI raised $150 million at a valuation of more than $1 billion, while gaming company Nex secured $150 million in combined equity and debt financing. Outside the AI-heavy group, Mazama Energy raised $135 million for superhot rock geothermal power and Sling Therapeutics closed a $123 million Series C for a small-molecule therapy for thyroid eye disease.
Data center developer Crusoe also formalized a previously reported raise of more than $3 billion, co-led by Atreides Management, Valor Equity Partners and Mubadala Capital. The funding activity was tracked for U.S.-based companies with rounds announced from Sept. 12 through Sept. 18, 2026, and the source notes that some deals may enter the database after a delay.