Mitsubishi does not post Contrast Ratio on any spec sheets but drilling into their FAQ section they actually answer the question:
"The Texas Instrument DLP chip we are using has a Contrast Ratio spec of 2500:1. Contrast ratios differ from screen size to screen size, and are also impacted by the amount of light in the room where the TV is being viewed."
Keep in mind that True Contrast ratio (rather than Dynamic Range Peak) beyond 2,000:1 is considered Excellent. The math becomes simple if the Dark Detailor takes it up four times then we're at 10,000:1 which is up there with the SXRD and Samsung - I'm presuming the 10K is Dynamic though since it's unlikely it could reach those levels otherwise since they both use the same DLP chip (Samsung)but perhaps the Mits processing takes it to another level as would the new screen on the 831 series.
Interesting they don't tout CR on any of the spec sheets and keep in mind 10K:1 isn't necessarily the limit several sets have been tested that surpass it - SXRD has tested out at 12-13K:1 and so I wouldn't think of 10K as a ceiling that the TV cannot go beyond they are estimates and it's not a good idea to overinflate those numbers as you leave your product vulnerable to bad press when evalulated by professional reviewers in the Lab.