You can find the image of the 64 bit Raspberry Pi OS at
You can download and flash it to a SD Card like any other image of the operating system. You should be able to run it on a RasPi that supports 64 bit. As far as I know, these are RPi 3B, 3B+, and 4B. There may be others, please give me a note.
But if you boot it, it hangs and just do nothing. This is because a Raspberry Pi loads a 32 bit kernel by default. You have to tell it to use the 64 bit kernel
/boot/kernel8.img. This can be done with an entry in
/boot/config.txt. Just mount the fat (boot) partition of the fresh flashed SD Card, attached to your "flashing machine", and add this line to it:
and have fun with 64 bit :-)
The link to the forum thread Raspberry Pi OS (64 bit) beta test version, given by @Nick in his comment (thanks to Nick), says what it is. As you can read there, it has some limitations and it is not official propagated.
Known issues at 2020-06-02
1. There is no hardware video acceleration in VLC or Chromium
2. libraspberrypi0, libraspberrypi-dev and libraspberrypi-doc have been moved out of /opt/vc/* and into /usr/* instead (making it more standard). Any code built against these libraries will require changing to refer to a more standard location (/usr/lib/ rather than /opt/vc/lib)
3. Due to 2) Many packages that expect libGLESv2.so libEGL etc will require rebuilding.
4. raspberrypi-bootloader and raspberrypi-kernel contain useless non-64bit binaries and is missing the work done to minimise the delay between files being deleted and installed to /boot
5. There is no Wolfram Mathematica built for AArch64
6. Minecraft shim layer requires rebuilding to cope with 2)
7. VLC needs rebuild (not available)
8. VNC server not rebuilt yet for 64bit