This is a release candidate targeting the upcoming RN 0.65 release.

Highlighted Changes

• A new concurrent garbage collector "Hades", which delivered up to 30x shorter GC pause time on 64-bit device and 14x shorter on 32-bit devices. At Facebook, we saw this improve some CPU-intensive workloads by 20%-50%. You can learn more about Hades here.
• ECMAScript Internationalization API Specification (ECMA-402, or Intl) was a long asking features https://github.com/facebook/hermes/issues/23#issuecomment-816126715. It is now built into Hermes on Android and enabled by default, with only 57-62K per API size overhead (compared to JSC's 6MiB). With this change, Hermes users no longer require locale polyfills. A big thank you to @mganandraj and other partners at Microsoft for driving the implementation to make this happen!
• Memory Improvements including SMI (Small Integer) and pointer compression that shrank the JavaScript heap by 30%
• Changes to Function.prototype.toString that fixed performance drop due to improper feature detection: https://github.com/facebook/hermes/issues/471#issuecomment-820123463