December 4th, 2014: For information on what's new in 1.0 RC4, see the release announcement.
The release is available in both the canary channel and the beta channel, so you can check for updates via Help > Check for Update... (on OSX, look in the Android Studio menu). This will download and install a patch rather than download a full IDE image. For all older other versions you will need to install it from scratch by installing one of the below .zip files.
We don't have updated installers for this build; just install RC3, and then patch update to RC4 from there:
Full installer (SDK bundle): https://dl.google.com/dl/android/studio/install/1.0.0-rc3/android-studio-bundle-135.1624504-windows.exe (813 MB)
Lean installer (no SDK bundle): https://dl.google.com/dl/android/studio/install/1.0.0-rc3/android-studio-ide-135.1624504-windows.exe (250 MB)
Or, just use the RC4 zip file:
https://dl.google.com/dl/android/studio/ide-zips/1.0.0-rc4/android-studio-ide-135.1626825-windows.zip (234 MB)