It's late, I'm ill, so I'm going to be lazy and just post the news from their site: "Final versions of the two new Gentium font families have been released - Gentium Basic and Gentium Book Basic. Both families include regular, italic, bold and bold italic weights, with Gentium Book Basic being overall heavier than original Gentium. 'Basic' refers to the character set, which is limited to only basic Latin characters plus a variety of the most common extended Latin letters and diacritics."
Source: Typophile