Move over, Back Bay, and take a hike, Financial District.

The epicenter of the Boston business community can no longer be found in the Hub, but rather across the Charles in Cambridge – at least when it comes to pricey office space.

For the skeptics, just check out some of the rents being bandied about in Kendall Square. Building owners in the lab- and office-packed Cambridge neighborhood are quoting $80 a square foot for prime space, with the sky the limit, tenant advisory firm Cresa Boston notes in a new report.

That is, when there is actually space to lease. The vacancy rate for office space in the Cambridge neighborhood is a practically air-tight 0.6 percent, Cresa notes.

In fact, it’s getting so crazy that one Kendall Square landlord even jokingly quoted a $100 a square foot rent to a broker.

“I wouldn’t be surprised to see that number continue to climb,” said Paul Delaney of Cresa Boston, adding “each new lease commands a higher asking price.”

Of course, $80 a square foot is not the average rent for Kendall Square, but rather the high end of the asking price for blocks of office space in some of the neighborhood’s top addresses.

Still, that pretty much smokes anything right now in the Financial District, which has taken years to recover from the Great Recession. The only thing comparable would be some of the top rents quoted for space in coveted towers in the Back Bay, like the Hancock. Of course, the Hancock is 60 stories. Height has long been considered a prerequisite for charging elite rents.

By contrast, the tallest building in Kendall Square is 17 stories – that’s more of a mid-rise than a high-rise.

The New Normal

But for Microsoft, Google, Novartis and a bevy of other blue chip tech and biotech companies, Kendall Square is where it’s at right now, the center of the business world in the booming Boston market and an international center for the life sciences sector. Now companies are willing to pay increasingly outrageous numbers for relatively unimpressive office digs that a decade ago would have been simply too stumpy to be considered Class A buildings.

Helping boost rents, in turn, has been a shortage of office space, with no new, large speculative office buildings taking shape in nearly 15 years in Kendall Square.

When Biorad recently rolled out a smaller, 64,000-square-foot office building, a venture capital firm and some smaller companies have scooped up the space. Rents there are said to be in the $70s a square foot.

“What we are seeing is that folks are becoming a little more immune to the increase in rents and just accepting that it’s the new normal,” said Ted Lyon, executive managing director and principal at commercial real estate firm Cassidy Turley, who leads the Cambridge team.

Heading Downtown

But it’s not only in rising rents that we are seeing the ascendance of Kendall Square as business capital for the Boston area, and, for that matter, the state as whole.

In another sign of the times, Boston’s Financial District and Downtown Crossing have effectively become submarkets for Cambridge.

Increasingly, tech firms priced out of Kendall Square are finding a refuge in these two once-mighty Hub neighborhoods, which in turn, are in the middle now of big transitions in their own right.

Sonos, which makes wireless hi-fi systems, recently moved out of Kendall Square and into 170,000 square feet at the Lafayette City Center in Downtown Crossing.

Low-rise space in various Financial District towers – which has languished for years as the district’s fortunes ebbed – has become a cost-effective alternative for a number of tech companies, Delaney said.

“The proximity to MIT and Harvard [and] the convenience of the Red Line continue to make Kendall Square attractive to growing technology companies, but at some point they get priced out,” he said.

But it’s more than just high office rents that loudly proclaim that Kendall Square has arrived at the top of the heap; it’s the substance as well.

It would be hard to argue that the life science and tech sectors are not the Bay State’s leading private sector growth engines, right alongside such long-standing mainstays as Boston’s teaching hospitals and its many colleges and universities.

With the gleaming new Liberty Mutual headquarters, Back Bay has taken over the role once held by the Financial District as the headquarters for insurers and other old line employers.

The Financial District, in turn, is struggling to reinvent itself, with its very name an outdated vestige of the time when a number of regional banks were based in Boston, a couple with their own towers.

Kendall Square is where it’s at now. And it has the crazy office rents to prove it.

Email: sbvanvoorhis@hotmail.com