The software maker plans to say more on its Web site around noon, but, as noted by enthusiast site Neowin, the code is already available from Microsoft's download center.
Among the new features in IE 8 is a browsing mode known as InPrivate, designed not to leave fingerprints on a PC.
With IE 8, Microsoft is hoping to regain some lost ground by adding features such as private browsing, improved security and a new type of add-ons, called accelerators.
On the security front, Microsoft is adding a cross-site scripting filter as well as protections against a type of attack known as clickjacking.
In an interview, IE general manager Dean Hachamovitch said that there will be little change between the release candidate and the final version, although he declined to say when the final version will be released.
"The ecosystem should expect the final candidate to behave like the release candidate," Hachamovitch said.
Internet Explorer 8 will work with Windows XP (Service Pack 2 or later) and Windows Vista. A version of IE 8 is also being built into Windows 7.
During her years at CNET News, Ina Fried has changed beats several times, changed genders once, and covered both of the Pirates of Silicon Valley. These days, most of her attention is focused on Microsoft. E-mail Ina at firstname.lastname@example.org.
By Ina Fried