IPOs are back, but for how long?

The first quarter is almost over, and despite Dropbox’s splashy debut on the public market earlier today, it was preceded by just two other U.S. tech companies to IPO in 2018: Cardlytics and Zscaler.

Will Dropbox turn things around? Will the fact that Spotify is readying its debut get the momentum going at long last?

It all depends on how Dropbox and Spotify perform and how they impact what’s known as the IPO window. When new issuers perform well, it typically swings wide open. When they don’t, well, it gets slammed shut.

At this point, it’s been four years since we had an IPO window big enough for a stream of companies to pass through. In 2013, 50 tech companies went public. In 2014, the number was 62. Things grew chillier after that, with just 31, 26 and 27 companies getting out the window in 2015, 2016 and 2017, respectively.

Why haven’t things warmed up again, particularly with a stunning 171 venture-backed “unicorns” waiting in the wings?

Some high-profile flops are one large factor. Last year, venture-backed darlings like Blue Apron and Snapchat braved the public markets, but it was public shareholders who had to keep a stiff upper lip as their shares abruptly sputtered. These kinds of scenarios can seriously spook pipeline companies and their advisors, particularly in the world of consumer tech.

The availability of late-stage capital is also making it far easier to stay private longer. With SoftBank’s $100 billion Vision Fund writing enormous checks to growth startups — and traditional venture funds reacting by raising their own gigantic venture funds — this trend is only expected to continue.

There are also plenty of sky-high valuations to consider. Startups were able to command numbers that weren’t necessarily tied to reality in 2014 to 2015. That makes the prospect of a public offering, at a potentially much smaller valuation, something to be put off as long as possible.

Still, IPO insiders think things shifted once again — that a growing number of companies will have the wind at their backs in 2018. They point to strong signals like Zscaler doubling on its first day of trading and Dropbox pricing above its IPO range as favorable signs of what’s to come. Indeed, they say that behind the scenes, a lot of prep work has already set the stage.

“The number of tech companies, across the spectrum, now meeting with (if not engaging) bankers and working with the auditors to be ‘IPO ready’ is very definitely on the upswing,” says Lise Buyer, an IPO consultant and partner at Class V Group. The “window is already wide open, and there is enormous pent-up demand at institutions for new companies that are priced reasonably.”

John Tuttle, global head of listings at the New York Stock Exchange, similarly says he expects “a strong year if market conditions hold constant.” He characterizes the pipeline for technology offerings as “strong,” particularly enterprise technology companies.

Tuttle also notes the growing number of far-flung tech companies looking to list their share in the U.S. Among these are three China-based companies with plans to raise hundreds of millions of dollars by selling American depositary shares in the not-too-distant future, including Bilibili, a nine-year-old, Shanghai, China-based anime video sharing platform; iQiyi, an eight-year-old Beijing-based video streaming service; and OneSmart, a 10-year-old, Shanghai, China-based K-12 after-school education provider.

Hardware-maker Xiaomi is expecting to stage a public offering both in the U.S. and in Hong Kong this year, too.

That’s saying nothing of the Canadian and Latin American companies that are offering shares to U.S. investors. Among them: Brazil’s payments business PagSeguro Digital; it went pubic in January on the NYSE.

So who’s next? Following Dropbox and Spotify, Zuora, the 11-year-old, cloud subscription management platform, has finally filed to go public. Another company to just file is Pivotal Software, a spinoff of EMC and VMware. DocuSign is on file confidentially. We’re also hearing that quite a few other enterprise technology companies are gearing up to go public.

Just don’t expect to see big consumer tech companies like Airbnb, Uber and Pinterest listing in 2018. A lot of these “decacorns” are planning to debut next year at the earliest, partly because they’ve raised enough money that they can’t afford to make mistakes at this point.

They’ve raised enough money that they can wait, too. That means the rest of us will have to wait alongside them.