[FSSDK-12546] prepare for release javascript-sdk v6.4.0

Author: jaeopt

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [6.4.0] - May 4, 2026
+
+### New Features
+
+**Feature Rollout**: Added support for Feature Rollouts, a new experiment type combining Targeted Delivery simplicity with A/B test measurement capabilities. Feature Rollouts enable progressive rollouts with full impact analytics, metric tracking, and confidence intervals. See [Feature Rollout docs](https://support.optimizely.com/hc/en-us/articles/45552846481037-Run-Feature-Rollouts-in-Feature-Experimentation) for more information.
+
+- Add Feature Rollout support ([#1140](https://github.com/optimizely/javascript-sdk/pull/1140))
+
 ## [6.3.1] - January 26, 2026
 
 ### Changed

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@optimizely/optimizely-sdk",
-  "version": "6.3.1",
+  "version": "6.4.0",
   "description": "JavaScript SDK for Optimizely Feature Experimentation, Optimizely Full Stack (legacy), and Optimizely Rollouts",
   "main": "./dist/index.node.min.js",
   "browser": "./dist/index.browser.es.min.js",