We know Amazon Web Services (AWS) is growing — a lot — but Amazon doesn't reveal specifics about that growth. Now, though, the company decided AWS is too important to keep lumping into the "Other" category.

So Amazon will start breaking out AWS results starting with the current quarter, CFO Tom Szkutak said during Thursday's fourth-quarter earnings call.

"Other" includes non-retail businesses such as advertising services and credit card co-branding deals, but it's probably dominated by AWS.

And "Other" is growing rapidly. For North America (and we do know AWS' results are contained in the North American piece of "Other"), the category came in with revenues of $1.7 billion in the fourth quarter, up 43 percent from the fourth quarter a year ago. For all of 2014, North American "Other" totaled $5.4 billion.

Amazon did offer up some bragging numbers around its cloud service. Thursday's earnings release says AWS has more than 1 million "active" customers, with usage growing nearly 90 percent compared with last year's fourth quarter.

AWS is hiring as well, priming itself for growth.

"We are investing very heavily. You see that certainly in our capex numbers [and in] the assets we're acquiring with some of our capital leases," Szkutak said during the earnings call.

Szkutak wouldn't comment on whether price cuts in cloud services are likely to continue. Last year saw cloud providers, Amazon and Google in particular, in a race to the bottom in terms of pricing; off the top of his head, Szkutak guessed that the number of price cuts AWS underwent was "in the high forties." Early signs this year point to the fight shifting to services and features; Google's deal today to provide services on VMware's vCloud Air might be signaling such a trend.

For its fourth quarter, which ended Dec. 31, Amazon — the whole company — reported revenues of $29.3 billion and net income of $214 million, or 45 cents per share. Wall Street had expected only 17 cents per share, according to Thomson Reuters.

For its fourth quarter a year ago, Amazon reported revenues of $25.6 billion and net income of $239 million, or 51 cents per share.

Amazon shares were up $41.38 (13%) at $353.16 in after-hours trading.