diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery.html b/tests/phpunit/data/blocks/fixtures/core__gallery.html
index 5e48c7e663..54f9991f88 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery.html
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery.html
@@ -1,14 +1,15 @@
-<!-- wp:core/gallery -->
-<ul class="wp-block-gallery columns-2 is-cropped">
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="title" />
-		</figure>
-	</li>
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="http://google.com/hi.png" alt="title" />
-		</figure>
-	</li>
-</ul>
-<!-- /wp:core/gallery -->
+<!-- wp:gallery {"linkTo":"none","className":"columns-2"} -->
+<figure class="wp-block-gallery has-nested-images columns-default is-cropped columns-2">
+	<!-- wp:image {"sizeSlug":"large","linkDestination":"none"} -->
+	<figure class="wp-block-image size-large">
+		<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="Image gallery image" />
+	</figure>
+	<!-- /wp:image -->
+
+	<!-- wp:image {"sizeSlug":"large","linkDestination":"none"} -->
+	<figure class="wp-block-image size-large">
+		<img src="http://google.com/hi.png" alt="Image gallery image" />
+	</figure>
+	<!-- /wp:image -->
+</figure>
+<!-- /wp:gallery -->
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery.json b/tests/phpunit/data/blocks/fixtures/core__gallery.json
index 8cfcc26d3b..0225422123 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery.json
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery.json
@@ -1,25 +1,44 @@
 [
-    {
-        "clientId": "_clientId_0",
-        "name": "core/gallery",
-        "isValid": true,
-        "attributes": {
-            "images": [
-                {
-                    "url": "https://cldup.com/uuUqE_dXzy.jpg",
-                    "alt": "title",
-                    "caption": ""
-                },
-                {
-                    "url": "http://google.com/hi.png",
-                    "alt": "title",
-                    "caption": ""
-                }
-            ],
-            "imageCrop": true,
-            "linkTo": "none"
-        },
-        "innerBlocks": [],
-        "originalContent": "<ul class=\"wp-block-gallery columns-2 is-cropped\">\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"http://google.com/hi.png\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n</ul>"
-    }
+	{
+		"name": "core/gallery",
+		"isValid": true,
+		"attributes": {
+			"images": [],
+			"ids": [],
+			"shortCodeTransforms": [],
+			"caption": "",
+			"imageCrop": true,
+			"fixedHeight": true,
+			"linkTo": "none",
+			"sizeSlug": "large",
+			"allowResize": false,
+			"className": "columns-2"
+		},
+		"innerBlocks": [
+			{
+				"name": "core/image",
+				"isValid": true,
+				"attributes": {
+					"url": "https://cldup.com/uuUqE_dXzy.jpg",
+					"alt": "Image gallery image",
+					"caption": "",
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": []
+			},
+			{
+				"name": "core/image",
+				"isValid": true,
+				"attributes": {
+					"url": "http://google.com/hi.png",
+					"alt": "Image gallery image",
+					"caption": "",
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": []
+			}
+		]
+	}
 ]
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery.parsed.json b/tests/phpunit/data/blocks/fixtures/core__gallery.parsed.json
index fc5c9e17d6..00a75f5f13 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery.parsed.json
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery.parsed.json
@@ -1,13 +1,45 @@
 [
-    {
-        "blockName": "core/gallery",
-        "attrs": {},
-        "innerBlocks": [],
-        "innerHTML": "\n<ul class=\"wp-block-gallery columns-2 is-cropped\">\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"http://google.com/hi.png\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n</ul>\n",
-        "innerContent": [
-            "\n<ul class=\"wp-block-gallery columns-2 is-cropped\">\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"http://google.com/hi.png\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n</ul>\n"
-        ]
-    },
+	{
+		"blockName": "core/gallery",
+		"attrs": {
+			"linkTo": "none",
+			"className": "columns-2"
+		},
+		"innerBlocks": [
+			{
+				"blockName": "core/image",
+				"attrs": {
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": [],
+				"innerHTML": "\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"Image gallery image\" />\n\t</figure>\n\t",
+				"innerContent": [
+					"\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"Image gallery image\" />\n\t</figure>\n\t"
+				]
+			},
+			{
+				"blockName": "core/image",
+				"attrs": {
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": [],
+				"innerHTML": "\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"http://google.com/hi.png\" alt=\"Image gallery image\" />\n\t</figure>\n\t",
+				"innerContent": [
+					"\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"http://google.com/hi.png\" alt=\"Image gallery image\" />\n\t</figure>\n\t"
+				]
+			}
+		],
+		"innerHTML": "\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped columns-2\">\n\t\n\n\t\n</figure>\n",
+		"innerContent": [
+			"\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped columns-2\">\n\t",
+			null,
+			"\n\n\t",
+			null,
+			"\n</figure>\n"
+		]
+	},
     {
         "blockName": null,
         "attrs": {},
@@ -17,4 +49,4 @@
             "\n"
         ]
     }
-]
+]
\ No newline at end of file
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery.serialized.html b/tests/phpunit/data/blocks/fixtures/core__gallery.serialized.html
index 5bf6ce819f..bc5d6be414 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery.serialized.html
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery.serialized.html
@@ -1,3 +1,3 @@
-<!-- wp:gallery -->
-<ul class="wp-block-gallery columns-2 is-cropped"><li class="blocks-gallery-item"><figure><img src="https://cldup.com/uuUqE_dXzy.jpg" alt="title"/></figure></li><li class="blocks-gallery-item"><figure><img src="http://google.com/hi.png" alt="title"/></figure></li></ul>
-<!-- /wp:gallery -->
+<!-- wp:gallery {"linkTo":"none","className":"columns-2"} -->
+<figure class="wp-block-gallery has-nested-images columns-default is-cropped columns-2"><!-- wp:image {"sizeSlug":"large","linkDestination":"none"} --><figure class="wp-block-image size-large"><img src="https://cldup.com/uuUqE_dXzy.jpg" alt="Image gallery image" /></figure><!-- /wp:image --><!-- wp:image {"sizeSlug":"large","linkDestination":"none"} --><figure class="wp-block-image size-large"><img src="http://google.com/hi.png" alt="Image gallery image" /></figure><!-- /wp:image --></figure>
+<!-- /wp:gallery -->
\ No newline at end of file
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery.server.html b/tests/phpunit/data/blocks/fixtures/core__gallery.server.html
index 21ddbc9489..a185c67cd7 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery.server.html
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery.server.html
@@ -1,14 +1,15 @@
 
-<ul class="wp-container-1 wp-block-gallery-1 wp-block-gallery columns-2 is-cropped">
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="title" />
-		</figure>
-	</li>
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="http://google.com/hi.png" alt="title" />
-		</figure>
-	</li>
-</ul>
+<figure class="wp-container-1 wp-block-gallery-1 wp-block-gallery has-nested-images columns-default is-cropped columns-2">
+	
+	<figure class="wp-block-image size-large">
+		<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="Image gallery image" />
+	</figure>
+	
+
+	
+	<figure class="wp-block-image size-large">
+		<img src="http://google.com/hi.png" alt="Image gallery image" />
+	</figure>
+	
+</figure>
 
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.html b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.html
index cf1f1bb43f..4f34167c17 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.html
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.html
@@ -1,14 +1,15 @@
-<!-- wp:core/gallery {"columns":1} -->
-<ul class="wp-block-gallery columns-1 is-cropped">
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="title" />
-		</figure>
-	</li>
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="http://google.com/hi.png" alt="title" />
-		</figure>
-	</li>
-</ul>
-<!-- /wp:core/gallery -->
+<!-- wp:gallery {"linkTo":"none","className":"columns-1"} -->
+<figure class="wp-block-gallery has-nested-images is-cropped columns-1" >
+	<!-- wp:image {"sizeSlug":"large","linkDestination":"none"} -->
+	<figure class="wp-block-image size-large">
+		<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="Image gallery image" />
+	</figure>
+	<!-- /wp:image -->
+
+	<!-- wp:image {"sizeSlug":"large","linkDestination":"none"} -->
+	<figure class="wp-block-image size-large">
+		<img src="http://google.com/hi.png" alt="Image gallery image" />
+	</figure>
+	<!-- /wp:image -->
+</figure>
+<!-- /wp:gallery -->
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.json b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.json
index b3daaa05f6..4523d16b20 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.json
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.json
@@ -1,26 +1,45 @@
 [
-    {
-        "clientId": "_clientId_0",
-        "name": "core/gallery",
-        "isValid": true,
-        "attributes": {
-            "images": [
-                {
-                    "url": "https://cldup.com/uuUqE_dXzy.jpg",
-                    "alt": "title",
-                    "caption": ""
-                },
-                {
-                    "url": "http://google.com/hi.png",
-                    "alt": "title",
-                    "caption": ""
-                }
-            ],
-            "columns": 1,
-            "imageCrop": true,
-            "linkTo": "none"
-        },
-        "innerBlocks": [],
-        "originalContent": "<ul class=\"wp-block-gallery columns-1 is-cropped\">\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"http://google.com/hi.png\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n</ul>"
-    }
+	{
+		"name": "core/gallery",
+		"isValid": true,
+		"attributes": {
+			"images": [],
+			"ids": [],
+			"shortCodeTransforms": [],
+			"caption": "",
+			"imageCrop": true,
+			"fixedHeight": true,
+			"linkTo": "none",
+			"sizeSlug": "large",
+			"allowResize": false,
+			"className": "columns-1",
+            "columns": 1
+		},
+		"innerBlocks": [
+			{
+				"name": "core/image",
+				"isValid": true,
+				"attributes": {
+					"url": "https://cldup.com/uuUqE_dXzy.jpg",
+					"alt": "Image gallery image",
+					"caption": "",
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": []
+			},
+			{
+				"name": "core/image",
+				"isValid": true,
+				"attributes": {
+					"url": "http://google.com/hi.png",
+					"alt": "Image gallery image",
+					"caption": "",
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": []
+			}
+		]
+	}
 ]
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.parsed.json b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.parsed.json
index 6f6e4b856d..d3d7c23893 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.parsed.json
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.parsed.json
@@ -1,15 +1,45 @@
 [
-    {
-        "blockName": "core/gallery",
-        "attrs": {
-            "columns": 1
-        },
-        "innerBlocks": [],
-        "innerHTML": "\n<ul class=\"wp-block-gallery columns-1 is-cropped\">\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"http://google.com/hi.png\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n</ul>\n",
-        "innerContent": [
-            "\n<ul class=\"wp-block-gallery columns-1 is-cropped\">\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n\t<li class=\"blocks-gallery-item\">\n\t\t<figure>\n\t\t\t<img src=\"http://google.com/hi.png\" alt=\"title\" />\n\t\t</figure>\n\t</li>\n</ul>\n"
-        ]
-    },
+	{
+		"blockName": "core/gallery",
+		"attrs": {
+			"linkTo": "none",
+			"className": "columns-1"
+		},
+		"innerBlocks": [
+			{
+				"blockName": "core/image",
+				"attrs": {
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": [],
+				"innerHTML": "\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"Image gallery image\" />\n\t</figure>\n\t",
+				"innerContent": [
+					"\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"Image gallery image\" />\n\t</figure>\n\t"
+				]
+			},
+			{
+				"blockName": "core/image",
+				"attrs": {
+					"sizeSlug": "large",
+					"linkDestination": "none"
+				},
+				"innerBlocks": [],
+				"innerHTML": "\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"http://google.com/hi.png\" alt=\"Image gallery image\" />\n\t</figure>\n\t",
+				"innerContent": [
+					"\n\t<figure class=\"wp-block-image size-large\">\n\t\t<img src=\"http://google.com/hi.png\" alt=\"Image gallery image\" />\n\t</figure>\n\t"
+				]
+			}
+		],
+		"innerHTML": "\n<figure class=\"wp-block-gallery has-nested-images is-cropped columns-1\" >\n\t\n\n\t\n</figure>\n",
+		"innerContent": [
+			"\n<figure class=\"wp-block-gallery has-nested-images is-cropped columns-1\" >\n\t",
+			null,
+			"\n\n\t",
+			null,
+			"\n</figure>\n"
+		]
+	},
     {
         "blockName": null,
         "attrs": {},
@@ -19,4 +49,4 @@
             "\n"
         ]
     }
-]
+]
\ No newline at end of file
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.serialized.html b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.serialized.html
index 183e484ec4..88464bedce 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.serialized.html
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.serialized.html
@@ -1,3 +1,3 @@
-<!-- wp:gallery {"columns":1} -->
-<ul class="wp-block-gallery columns-1 is-cropped"><li class="blocks-gallery-item"><figure><img src="https://cldup.com/uuUqE_dXzy.jpg" alt="title"/></figure></li><li class="blocks-gallery-item"><figure><img src="http://google.com/hi.png" alt="title"/></figure></li></ul>
-<!-- /wp:gallery -->
+<!-- wp:gallery {"linkTo":"none","className":"columns-1"} -->
+<figure class="wp-block-gallery has-nested-images is-cropped columns-1"><!-- wp:image {"sizeSlug":"large","linkDestination":"none"} --><figure class="wp-block-image size-large"><img src="https://cldup.com/uuUqE_dXzy.jpg" alt="Image gallery image" /></figure><!-- /wp:image --><!-- wp:image {"sizeSlug":"large","linkDestination":"none"} --><figure class="wp-block-image size-large"><img src="http://google.com/hi.png" alt="Image gallery image" /></figure><!-- /wp:image --></figure>
+<!-- /wp:gallery -->
\ No newline at end of file
diff --git a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.server.html b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.server.html
index 9460b2e09e..4056203589 100644
--- a/tests/phpunit/data/blocks/fixtures/core__gallery__columns.server.html
+++ b/tests/phpunit/data/blocks/fixtures/core__gallery__columns.server.html
@@ -1,14 +1,15 @@
 
-<ul class="wp-container-1 wp-block-gallery-1 wp-block-gallery columns-1 is-cropped">
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="title" />
-		</figure>
-	</li>
-	<li class="blocks-gallery-item">
-		<figure>
-			<img src="http://google.com/hi.png" alt="title" />
-		</figure>
-	</li>
-</ul>
+<figure class="wp-container-1 wp-block-gallery-1 wp-block-gallery has-nested-images is-cropped columns-1" >
+	
+	<figure class="wp-block-image size-large">
+		<img src="https://cldup.com/uuUqE_dXzy.jpg" alt="Image gallery image" />
+	</figure>
+	
+
+	
+	<figure class="wp-block-image size-large">
+		<img src="http://google.com/hi.png" alt="Image gallery image" />
+	</figure>
+	
+</figure>