Following last week's rumors of Comcast gearing up to offer 305Mbps cable broadband, the company has officially confirmed speculation. Labeled as Xfinity Platinum, Comcast has announced it is actually in the process of rolling out the speedy Internet service to "many major markets". The company will also be doubling the speeds of their 25Mbps and 50Mbps plans for existing subscribers at no additional cost.

The new Xfinity Platinum service promises 305Mbps down and 65Mbps up but no pricing details have emerged. Verizon offers its 300Mbps FiOS service for about $210 though, so there is some expectation that Comcast will hit a similar price point. "Blast" and "Extreme" subscribers who have enjoyed 25Mbps and 50Mbps tiers will see their top speeds doubled to 50Mbps and 105Mbps, respectively -- at no additional cost.

We’re doubling the speed of the Blast tier from 25 to 50 Mbps and the price does not change. It is $58.95/month multi-product or $72.95/month standalone. We’re also (more than) doubling Extreme 50 from 50 Mbps to 105 Mbps and the price also does not change. It is $99.95/mo multi-product or $114.95/month standalone (prices may vary by market).

Source: gigaom.com

It is interesting to note that Comcast offers 305Mbps instead of 300Mbps, one-upping its competitor for bragging rights as the fastest national ISP in the U.S.

Although "many major markets" is nothing short of unsatisifactorily vague, the press release does specifically list Boston, Hartford, Philadelphia, Pittsburgh, Harrisburg, Wilmington, Baltimore, Washington, D.C., Richmond, and New Jersey. The wording implies that other areas may be receiving the upgrades too, but there's no way to know for certain.

Comcast has long been criticized for imposing an artificial data impasse of 250GB per month on all of its residential plans. However, the hard cap was lifted in May -- although perhaps only temporarily -- while Comcast continues to mull over plans of introducing a beefier 300GB per month soft cap. Unlike the 250GB cap, subscribers would be able to exceed that amount albeit at a nominal fee.