diff --git a/starpunk/feeds/atom.py b/starpunk/feeds/atom.py
index 8df3fc7..3935ef3 100644
--- a/starpunk/feeds/atom.py
+++ b/starpunk/feeds/atom.py
@@ -184,12 +184,18 @@ def generate_atom_streaming(
                 yield f'    <category term="{_escape_xml(tag["name"])}" label="{_escape_xml(tag["display_name"])}"/>\n'
 
         # Media enclosures (v1.2.0 Phase 3, per Q24 and ADR-057)
+        # Enhanced with title attribute for captions (v1.4.0 Phase 4)
         if hasattr(note, 'media') and note.media:
             for item in note.media:
                 media_url = f"{site_url}/media/{item['path']}"
                 mime_type = item.get('mime_type', 'image/jpeg')
                 size = item.get('size', 0)
-                yield f'    <link rel="enclosure" type="{_escape_xml(mime_type)}" href="{_escape_xml(media_url)}" length="{size}"/>\n'
+                caption = item.get('caption', '')
+
+                # Include title attribute for caption
+                title_attr = f' title="{_escape_xml(caption)}"' if caption else ''
+
+                yield f'    <link rel="enclosure" type="{_escape_xml(mime_type)}" href="{_escape_xml(media_url)}" length="{size}"{title_attr}/>\n'
 
         # Content - include media as HTML (per Q24)
         if note.html:
diff --git a/starpunk/feeds/json_feed.py b/starpunk/feeds/json_feed.py
index 16b1783..a58348d 100644
--- a/starpunk/feeds/json_feed.py
+++ b/starpunk/feeds/json_feed.py
@@ -313,12 +313,46 @@ def _build_item_object(site_url: str, note: Note) -> Dict[str, Any]:
     if hasattr(note, 'tags') and note.tags:
         item["tags"] = [tag['display_name'] for tag in note.tags]
 
-    # Add custom StarPunk extensions
-    item["_starpunk"] = {
+    # Add custom StarPunk extensions (v1.4.0 Phase 4)
+    from flask import current_app
+    about_url = current_app.config.get(
+        "STARPUNK_ABOUT_URL",
+        "https://github.com/yourusername/starpunk"
+    )
+    starpunk_ext = {
         "permalink_path": note.permalink,
-        "word_count": len(note.content.split())
+        "word_count": len(note.content.split()),
+        "about": about_url
     }
 
+    # Add media variants if present
+    if hasattr(note, 'media') and note.media:
+        media_variants = []
+
+        for media_item in note.media:
+            variants = media_item.get('variants', {})
+
+            if variants:
+                media_info = {
+                    "caption": media_item.get('caption', ''),
+                    "variants": {}
+                }
+
+                for variant_type, variant_data in variants.items():
+                    media_info["variants"][variant_type] = {
+                        "url": f"{site_url}/media/{variant_data['path']}",
+                        "width": variant_data['width'],
+                        "height": variant_data['height'],
+                        "size_in_bytes": variant_data['size_bytes']
+                    }
+
+                media_variants.append(media_info)
+
+        if media_variants:
+            starpunk_ext["media_variants"] = media_variants
+
+    item["_starpunk"] = starpunk_ext
+
     return item
 
 
diff --git a/starpunk/feeds/rss.py b/starpunk/feeds/rss.py
index 35153e7..80d72e9 100644
--- a/starpunk/feeds/rss.py
+++ b/starpunk/feeds/rss.py
@@ -304,18 +304,62 @@ def generate_rss_streaming(
                 item_xml += f"""
       <category>{_escape_xml(tag['display_name'])}</category>"""
 
-        # Add media:content elements (all images)
+        # Enhanced media handling with variants (v1.4.0 Phase 4)
         if hasattr(note, 'media') and note.media:
             for media_item in note.media:
-                media_url = f"{site_url}/media/{media_item['path']}"
-                item_xml += f"""
-      <media:content url="{_escape_xml(media_url)}" type="{media_item.get('mime_type', 'image/jpeg')}" medium="image" fileSize="{media_item.get('size', 0)}"/>"""
+                variants = media_item.get('variants', {})
 
-            # Add media:thumbnail (first image only)
-            first_media = note.media[0]
-            media_url = f"{site_url}/media/{first_media['path']}"
-            item_xml += f"""
-      <media:thumbnail url="{_escape_xml(media_url)}"/>"""
+                # Use media:group for multiple sizes of same image
+                if variants:
+                    item_xml += '\n      <media:group>'
+
+                    # Determine which variant is the default (largest available)
+                    # Fallback order: large -> medium -> small
+                    default_variant = None
+                    for fallback in ['large', 'medium', 'small']:
+                        if fallback in variants:
+                            default_variant = fallback
+                            break
+
+                    # Add each variant as media:content
+                    for variant_type in ['large', 'medium', 'small']:
+                        if variant_type in variants:
+                            v = variants[variant_type]
+                            media_url = f"{site_url}/media/{v['path']}"
+                            is_default = 'true' if variant_type == default_variant else 'false'
+                            item_xml += f'''
+        <media:content url="{_escape_xml(media_url)}"
+                       type="{media_item.get('mime_type', 'image/jpeg')}"
+                       medium="image"
+                       isDefault="{is_default}"
+                       width="{v['width']}"
+                       height="{v['height']}"
+                       fileSize="{v['size_bytes']}"/>'''
+
+                    item_xml += '\n      </media:group>'
+
+                    # Add media:thumbnail
+                    if 'thumb' in variants:
+                        thumb = variants['thumb']
+                        thumb_url = f"{site_url}/media/{thumb['path']}"
+                        item_xml += f'''
+      <media:thumbnail url="{_escape_xml(thumb_url)}"
+                       width="{thumb['width']}"
+                       height="{thumb['height']}"/>'''
+
+                    # Add media:title for caption
+                    if media_item.get('caption'):
+                        item_xml += f'''
+      <media:title type="plain">{_escape_xml(media_item['caption'])}</media:title>'''
+
+                else:
+                    # Fallback for media without variants (legacy)
+                    media_url = f"{site_url}/media/{media_item['path']}"
+                    item_xml += f'''
+      <media:content url="{_escape_xml(media_url)}"
+                     type="{media_item.get('mime_type', 'image/jpeg')}"
+                     medium="image"
+                     fileSize="{media_item.get('size', 0)}"/>'''
 
         # Close item
         item_xml += """
diff --git a/tests/test_feeds_rss.py b/tests/test_feeds_rss.py
index 22b7f35..80691ae 100644
--- a/tests/test_feeds_rss.py
+++ b/tests/test_feeds_rss.py
@@ -402,7 +402,7 @@ class TestRSSStreamingMedia:
             assert enclosure is not None
 
     def test_rss_streaming_includes_media_elements(self, app, note_with_single_media):
-        """Streaming RSS should include media:content and media:thumbnail"""
+        """Streaming RSS should include media:content and media:thumbnail (v1.4.0 with variants)"""
         with app.app_context():
             generator = generate_rss_streaming(
                 site_url="https://example.com",
@@ -419,8 +419,10 @@ class TestRSSStreamingMedia:
             channel = root.find("channel")
             item = channel.find("item")
 
-            media_content = item.find("media:content", namespaces)
-            media_thumbnail = item.find("media:thumbnail", namespaces)
+            # v1.4.0: media:content is now inside media:group for images with variants
+            # Use // to search descendants, not direct children
+            media_content = item.find(".//media:content", namespaces)
+            media_thumbnail = item.find(".//media:thumbnail", namespaces)
 
             assert media_content is not None
             assert media_thumbnail is not None