Amazon has had a big secret for years. Now suddenly, it's coming clean.

You might have noticed that Amazon pushes the Echo and its Alexa voice activated system, very hard. The premium real estate at the top of the home page is taken up with an Echo or Echo Dot more often than not, and the company offers continual steep discounts.

But ever since its introduction in 2014, Amazon has simply been unwilling to reveal exactly how many Alexa equipped units it's sold.

They've held this number more closely than perhaps any other secret--at least since the days when people were clamoring to know how many Kindles Amazon sold (but Amazon just wouldn't say).

Now the numbers can be told, apparently. Amazon has sold "100 million devices with Alexa on board," as Amazon's senior vice president of devices and services, Dave Limp revealed to writer Dieter Bohn of The Verge.

Limp also revealed that Amazon beat its expectation for sales of the smaller Echo Dot during the holidays, but wouldn't give hard numbers there. (Old habits die hard, I guess.)

But setting aside the Dot, why the change of heart? And, is 100 million a good number or not? According to Bohn, it seems like the second question provides part of the answer to the first.

Selling 100 million of anything is pretty fantastic, unless you were to compare it to the number of devices sold with Apple's Siri, or Google Assist.

But, are people buying the iPhone or an Android phone for the assistant alone? Probably not; but they are buying Amazon Echoes for basically no other reason than the Alexa technology.

"Depending on how you count, it's either seriously impressive or a serious problem for Amazon," Bohn writes. 

As for why Amazon would reveal the number now, well, it's in advance of CES, the big consumer electronics convention in Las Vegas. 

While Limp insists he doesn't think that Amazon, Apple, or Google will completely dominate voice-activated platforms in the near term, both of those other companies have big presences at CES. Apple even took out a full-size billboard overlooking the convention.

Amazon hasn't traditionally had as much of a presence. But this year, it appears perhaps it's making a bit of a splash by releasing a bit of closely held information. 

"Customers do not care about an ad campaign on the Las Vegas Strip," he said. "They just don't. It's playing to the industry. It's not playing to who really matters."