diff --git a/wp-includes/block-supports/layout.php b/wp-includes/block-supports/layout.php
index 98b44079ba..4e19785318 100644
--- a/wp-includes/block-supports/layout.php
+++ b/wp-includes/block-supports/layout.php
@@ -34,6 +34,7 @@ function wp_register_layout_support( $block_type ) {
  *
  * @since 5.9.0
  * @since 6.1.0 Added `$block_spacing` param, use style engine to enqueue styles.
+ * @since 6.3.0 Added grid layout type.
  * @access private
  *
  * @param string               $selector                      CSS selector.
@@ -287,6 +288,44 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
 				);
 			}
 		}
+	} elseif ( 'grid' === $layout_type ) {
+		if ( ! empty( $layout['columnCount'] ) ) {
+			$layout_styles[] = array(
+				'selector'     => $selector,
+				'declarations' => array( 'grid-template-columns' => 'repeat(' . $layout['columnCount'] . ', minmax(0, 1fr))' ),
+			);
+		} else {
+			$minimum_column_width = ! empty( $layout['minimumColumnWidth'] ) ? $layout['minimumColumnWidth'] : '12rem';
+
+			$layout_styles[] = array(
+				'selector'     => $selector,
+				'declarations' => array( 'grid-template-columns' => 'repeat(auto-fill, minmax(min(' . $minimum_column_width . ', 100%), 1fr))' ),
+			);
+		}
+
+		if ( $has_block_gap_support && isset( $gap_value ) ) {
+			$combined_gap_value = '';
+			$gap_sides          = is_array( $gap_value ) ? array( 'top', 'left' ) : array( 'top' );
+
+			foreach ( $gap_sides as $gap_side ) {
+				$process_value = is_string( $gap_value ) ? $gap_value : _wp_array_get( $gap_value, array( $gap_side ), $fallback_gap_value );
+				// Get spacing CSS variable from preset value if provided.
+				if ( is_string( $process_value ) && str_contains( $process_value, 'var:preset|spacing|' ) ) {
+					$index_to_splice = strrpos( $process_value, '|' ) + 1;
+					$slug            = _wp_to_kebab_case( substr( $process_value, $index_to_splice ) );
+					$process_value   = "var(--wp--preset--spacing--$slug)";
+				}
+				$combined_gap_value .= "$process_value ";
+			}
+			$gap_value = trim( $combined_gap_value );
+
+			if ( null !== $gap_value && ! $should_skip_gap_serialization ) {
+				$layout_styles[] = array(
+					'selector'     => $selector,
+					'declarations' => array( 'gap' => $gap_value ),
+				);
+			}
+		}
 	}
 
 	if ( ! empty( $layout_styles ) ) {
diff --git a/wp-includes/class-wp-theme-json.php b/wp-includes/class-wp-theme-json.php
index 700cb20f7e..c157b2462c 100644
--- a/wp-includes/class-wp-theme-json.php
+++ b/wp-includes/class-wp-theme-json.php
@@ -1370,7 +1370,7 @@ class WP_Theme_JSON {
 
 				if (
 					! empty( $class_name ) &&
-					! empty( $base_style_rules )
+					is_array( $base_style_rules )
 				) {
 					// Output display mode. This requires special handling as `display` is not exposed in `safe_style_css_filter`.
 					if (
diff --git a/wp-includes/theme.json b/wp-includes/theme.json
index 581bdb0b32..650072457d 100644
--- a/wp-includes/theme.json
+++ b/wp-includes/theme.json
@@ -332,6 +332,28 @@
 							}
 						}
 					]
+				},
+				"grid": {
+					"name": "grid",
+					"slug": "grid",
+					"className": "is-layout-grid",
+					"displayMode": "grid",
+					"baseStyles": [
+						{
+							"selector": " > *",
+							"rules": {
+								"margin": "0"
+							}
+						}
+					],
+					"spacingStyles": [
+						{
+							"selector": "",
+							"rules": {
+								"gap": null
+							}
+						}
+					]
 				}
 			}
 		},
diff --git a/wp-includes/version.php b/wp-includes/version.php
index c76eb599df..a5c30f3507 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-alpha-55974';
+$wp_version = '6.3-alpha-55975';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.