Company insiders and Wzor have confirmed that 7100 is the official Windows 7 RC build.
7100.0.winmain_win7rc.090421-1700 was compiled on Tuesday and has reportedly been handed out to OEM partners and TAP gold customers. Earlier this month we reported that build 7077 had leaked online and that Microsoft were pushing towards a 7100 RC release.
Microsoft recently published details about a public RC due for May 5th. We expect MSDN/TechNet customers to receive the bits within the next week if the company is still targeting May 5th.
According to reports, 7115.0.winmain.090421-1650 is the latest build internally at the time of writing.