The number of private tech companies valued at $1 billion or more has surged so much this year that on average 1.3 so-called "unicorn" companies have been created every week in 2015.

And in spite of Silicon Valley insiders' fears of a tech bubble, that number doesn't seem to be declining.

A new report from CB Insights and KPMG, released Wednesday, examined venture capital activity in the third quarter of 2015.

The big takeaway: just 9 months into 2015, $57.9 billion has been invested into US startups.

For context, that's already more than the total amount of venture capital funding invested into US startups in 2014 ($56.5 billion).

More unicorns are born

The third quarter of 2015 also doubled in the volume of new unicorns compared to the same quarter last year. Q3 2015 saw the addition of 17 new US unicorns and 3 new Asian ones, including companies like subscription food delivery service HelloFresh, Thumbtack, and Carbon3D.

In total, according to CB Insights, there are 140 billion-dollar "unicorn" companies globally with a cumulative valuation of $503 billion.

The number of mega-rounds of funding, which are defined as worth more than $100 million, has risen 125% from a year ago. Companies like Uber and DraftKings were among those who raised 37 $100 million mega-rounds in the past three months.

Tech's unicorns have been breeding — but they're not making exits in the form of IPOs, possibly because it's just so easy to raise private capital right now.

Seed investments have dipped, and are at a five-quarter low, CB Insights says. This may be due to an influx of late-stage deals and fewer IPO exits than in previous years.

Is this as good as it gets?

Recently, there's been an increase in chatter among insiders about a growing tech bubble. Investors are worried that fast-growing startups have been too reliant on easy venture capital for too long. Their customer acquisition costs are too high, their customer and user growth numbers are increasing because they're depending on VC funding to help them expand into new markets, and all the while they're bleeding cash.

In addition, late-stage rounds of funding are getting more difficult to raise without revenue growth and a path to profitability.

There's been a growing sense that the Fed could soon raise interest rates, which would impact startup investing. More importantly: Successful VC-backed tech sector IPOs have been few and far between. Last week, flash-storage provider Pure Storage went public, but began trading below its $17 IPO price, and closed the day at $16.01.

The public markets are much harsher than private markets. This means private investors need to reset their expectations, which is leading to downward valuation pressure.