Tech’s most valuable players today crossed the $3 trillion aggregate market cap mark according to Google Finance data. It’s a feat that marks a new threshold for tech amidst the current boom.

As “Nasdaq 5,000” was a critical moment in the dot-com rally, the $3 trillion result for the firms that we call the “Big 5” is notable. This is largely because the biggest tech companies — ranked by market cap, as revenue comes in varying quality — have helped fuel the growth of various indices that are setting records themselves.

The current market rally is, in some ways, a technology rally. Let’s examine the number, how we got here and why it matters.

$3 trillion and counting

According to our public spreadsheet that sources data from Google Finance, the Big 5 (Apple, Alphabet, Amazon, Facebook, Microsoft) are worth $3.03 trillion when combined. To double-check that number, we ran the same count with Yahoo Finance, summing to a $3.002 trillion.

(Wolfram Alpha, which we’ll get to in a moment, spits out a result of $2.978 trillion. So we’re two for two on the result totaling $3 trillion or more, and one for one that easily rounds up. Not bad.)

To reach today’s threshold, the Big 5 had to go on a lengthy tear. Here are their gains, as measured from their respective 52-week lows:

Apple: 56.63 percent

Amazon: 44.61 percent

Facebook: 44.55 percent

Microsoft: 39.54 percent

Alphabet: 33.45 percent

When you measure down from 52-week highs, the group’s laggard is Apple, off 3.59 percent. Alphabet is closest to the metal, off just 0.24 percent. What matters, however, is that their collective rally has reached a new watermark, not that any one company is “ahead.”

So why do we care?

Why this matters

As mentioned in our opening paragraphs, the setting of new thresholds is something often done in peak moments, or at least periods when things are better than normal. For tech, that’s now.

We’re racing around what we said about the matter in May, which we should quote here:

But the Big 5 are rapidly approaching thirteen-digit club. If the largest tech companies manage to reach that value mark in the current business cycle, and before its turn, it will be interesting to see if it will be the new Nasdaq 5,000, a prior psychological barrier set during the first dotcom boom, and it was only recently put to bed as hopelessly dated.

Now, a few months later, they’ve made it.

The moment comes despite some tension in the tech industry. Despite, say, chop among some previously high-flying private tech companies — shutdowns, layoffs, Theranos — and some unicorns that are going public — Blue Apron, Tintri — things are buoyant in broader tech. And after a long rally marked recently by sharp share price gains among the largest tech companies, the $3 trillion mark could stand up over time as a good thumb-sized measurement to vet future rallies against.

And, perhaps, even more, it can help us understand how concentrated the tech industry is at any given point. In the era of platform players racing to control the digital lives of both consumers and enterprises, it’s perhaps not surprising that the biggest companies are worth so very much; if the tech industry changes, becoming more fractured, that could shift. (We would need to do separate work to create a Gini coefficient for tech market cap, but the general point stands.)

For fun, here’s the chart, via the excellent Wolfram Alpha, that shows the aggregate change in value of the Big 5 over time:

(As you can see, earlier in the year, the Big 5 flirted with $3 trillion. But we never saw the $3 trillion mark reached at market-close until today.)

Good times (for now)

The situation throws light on a number of things we discuss in the pages of Crunchbase News, which are largely dedicated to private companies and their financials.

We can distill it into two parts:

It could help drive M&A activity in the sector. If M&A currently disappoints, something that is niche-dependent inside of the sector, this milestone may not excite you. After all, if companies are flush and not buying, what will happen when their market cap is cut by, say, 20 percent? Moral: M&A could get a lot worse.

The gap between private and public valuations is still yawning. Fewer unicorns are going public this year than expected, and there have been valuation cuts required to get some offerings out the door. Similar to our first point: If this is as good as it gets for IPOs when markets are hot, it may not bode well as to what will come when market conditions fluctuate.

In sum: It’s a big day for tech’s biggest players, even if it isn’t the most intriguing of them all or the simplest to explain.

We’ll keep an eye on the Big 5 and see how high they can get before the market decides to run a little profit taking.