The Series B Pipeline Looks Refreshingly Diversified

Before pulling data, one usually has a preconceived idea of what the results will show. In this case, looking at recent U.S. Series B investments, my assumption was that big rounds would be dominated by a few buzzy AI sectors.

The reality, however, looks far more diversified. Startups securing the largest rounds run the gamut from biotech to robotics to security and more. Obviously AI is the leading theme, but the pipeline of funded companies is anything but cookie-cutter.

Overall funding levels also look fairly healthy, with annual Series B funding moving steadily higher after hitting a low in 2023. This year is off to a strong start as well, as charted below.

Round counts are also holding up at a steady level, an encouraging indicator for those worried about capital concentration thinning the ranks of funded companies. It may be happening at late stage, but Series B is not so dramatically affected.

Investor favorites

Even so, a good chunk of Series B investment did go to a handful of favored startups.

Looking at rounds from the past six months, the largest was a $2 billion Nvidia-led financing for Reflection AI, a developer of open foundation models founded in 2024 by former Google DeepMind researchers.

Another standout was Kailera Therapeutics, which is developing oral treatments for obesity. The then year-old company raised $600 million in October. Physical Intelligence, an AI robotics startup, also raised $600 million in a November Series B led by Google’s CapitalG.

For a bigger-picture view, we used Crunchbase data to put together a list of 10 of the largest Series B recipients of the past six months.

Round sizes grow bigger

Another trend we’re seeing is that average round sizes are getting larger. So far in 2026, for instance, the average Series B is $68 million, which appears to be the highest on record.

As you can see charted below, the average size of a Series B round has been inching higher for a few years. It’s not as pronounced as what we’re seeing at later-stage, which continues to set fresh records for deal size. But still, investors are putting more capital into their largest deals.

Meanwhile, smaller Series B rounds are scarcer. From 2020 through 2023, for instance, there were typically about 150 rounds of between $1 million and $10 million each year. Last year, there were only 44 such rounds.

Still plenty of variety

While Series B investors may be consolidating their bets somewhat, they’re doing so across a wide range of sectors and technologies.

Per Crunchbase data, more than a quarter of Series B funding over the past six months has gone to healthcare and biotech startups. About 15% has gone to robotics and hardware-related investments.

Roughly half of Series B investment for the past six months also went to companies in AI-related categories across multiple industries. In addition, a majority of investment went to software-focused companies.

At this stage and typical size, one can assume investors are no longer making risky bets on unproven upstarts. To get to Series B requires some impressive technological edge, early traction, or both. And for most, they’re just getting started.