diff --git a/.github/workflows/test-old-branches.yml b/.github/workflows/test-old-branches.yml
index 6b5a323d5a..603e585cde 100644
--- a/.github/workflows/test-old-branches.yml
+++ b/.github/workflows/test-old-branches.yml
@@ -34,12 +34,14 @@ jobs:
             'test-npm.yml'
         ]
         branch: [
-            '6.2', '6.1','6.0',
+            '6.3', '6.2', '6.1','6.0',
             '5.9', '5.8', '5.7', '5.6', '5.5', '5.4', '5.3', '5.2', '5.1', '5.0',
             '4.9', '4.8', '4.7', '4.6', '4.5', '4.4', '4.3', '4.2', '4.1'
         ]
         include:
           # PHP Compatibility testing was introduced in 5.5.
+          - branch: '6.3'
+            workflow: 'php-compatibility.yml'
           - branch: '6.2'
             workflow: 'php-compatibility.yml'
           - branch: '6.1'
@@ -60,6 +62,8 @@ jobs:
           # End-to-end testing was introduced in 5.3 but was later removed as there were no meaningful assertions.
           # Starting in 5.8 with #52905, some additional tests with real assertions were introduced.
           # Branches 5.8 and newer should be tested to confirm no regressions are introduced.
+          - branch: '6.3'
+            workflow: 'end-to-end-tests.yml'
           - branch: '6.2'
             workflow: 'end-to-end-tests.yml'
           - branch: '6.1'
@@ -72,6 +76,8 @@ jobs:
             workflow: 'end-to-end-tests.yml'
 
           # Performance testing was introduced in 6.2.
+          - branch: '6.3'
+            workflow: 'performance.yml'
           - branch: '6.2'
             workflow: 'performance.yml'
 
@@ -79,7 +85,7 @@ jobs:
     steps:
       - name: Dispatch workflow run
         uses: actions/github-script@98814c53be79b1d30f795b907e553d8679345975 # v6.4.0
-        if: ${{ github.event_name == 'push' || github.event.schedule == '0 0 15 * *' || matrix.branch == '6.2' }}
+        if: ${{ github.event_name == 'push' || github.event.schedule == '0 0 15 * *' || matrix.branch == '6.3' }}
         with:
           retries: 2
           retry-exempt-status-codes: 418
diff --git a/SECURITY.md b/SECURITY.md
index 2c2ceb8249..7d9e4b9368 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -10,6 +10,7 @@ Full details of the WordPress Security Policy and the list of covered projects a
 
 | Version | Supported |
 | ------- | --------- |
+| 6.3.x   | Yes       |
 | 6.2.x   | Yes       |
 | 6.1.x   | Yes       |
 | 6.0.x   | Yes       |
diff --git a/package-lock.json b/package-lock.json
index 275c5f9214..f5d55dbdd7 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
 	"name": "WordPress",
-	"version": "6.3.0",
+	"version": "6.4.0",
 	"lockfileVersion": 1,
 	"requires": true,
 	"dependencies": {
diff --git a/package.json b/package.json
index e78fb5bfd8..e49427e5c3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "WordPress",
-	"version": "6.3.0",
+	"version": "6.4.0",
 	"description": "WordPress is open source software you can use to create a beautiful website, blog, or app.",
 	"repository": {
 		"type": "svn",
diff --git a/src/wp-includes/version.php b/src/wp-includes/version.php
index 1e8c513560..a58fa72d4b 100644
--- a/src/wp-includes/version.php
+++ b/src/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-RC1-56265-src';
+$wp_version = '6.4-alpha-56267-src';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.