The new 64-bit version takes advantage of OS X's 64-bit architecture, offering performance and security improvements that are not possible with the current 32-bit Chrome for Mac release. While there are several changes under the hood, the most notable difference to users will be the faster initial launch of the Chrome browser and a decrease in overall system memory usage by the browser.
Starting today, Mac owners can download this 64-bit version from Google's Chrome beta channel. The 64-bit Chrome beta for OS X is compatible with all Macs that have a 64-bit processor, which includes most modern Mac hardware. You can view this Apple support document for instructions on how to locate your processor type and determine whether it is 32-bit or 64-bit.
Remember, this 64-bit version of Chrome is still in beta, which means it may still have some stability issues. These beta versions are used to test new features before they are included in the public version of Chrome. If all goes smoothly, we should see 64-bit support roll out in the public Chrome build in the near future.