No official announcement yet, but the ReSharper 4.0 Nightly Build page is showing the first build marked as stable and with the status "Beta Candidate".
The build number is 804.
Off to downloading it: let's hope they fixed all the problems and the huge memory requirements of the latest builds.
UPDATE: JetBrains officially announced ReSharper beta
Technorati Tag: Resharper 4,Beta