diff --git a/packages/js/api-core-tests/composer.json b/packages/js/api-core-tests/composer.json
index 8722063d1f8..059a937b966 100644
--- a/packages/js/api-core-tests/composer.json
+++ b/packages/js/api-core-tests/composer.json
@@ -10,7 +10,7 @@
 	"extra": {
 		"changelogger": {
 			"formatter": {
-				"class": "PackageFormatter"
+				"filename": "../../../tools/changelogger/PackageFormatter.php"
 			},
 			"types": [
 				"Fix",
@@ -23,10 +23,5 @@
 			],
 			"changelog": "NEXT_CHANGELOG.md"
 		}
-	},
-	"autoload": {
-		"files": [
-			"../../../tools/changelogger/PackageFormatter.php"
-		]
 	}
 }
diff --git a/packages/js/api/composer.json b/packages/js/api/composer.json
index a1083a421ce..d5ea2d1d861 100644
--- a/packages/js/api/composer.json
+++ b/packages/js/api/composer.json
@@ -10,7 +10,7 @@
 	"extra": {
 		"changelogger": {
 			"formatter": {
-				"class": "PackageFormatter"
+				"filename": "../../../tools/changelogger/PackageFormatter.php"
 			},
 			"types": [
 				"Fix",
@@ -23,10 +23,5 @@
 			],
 			"changelog": "NEXT_CHANGELOG.md"
 		}
-	},
-	"autoload": {
-		"files": [
-			"../../../tools/changelogger/PackageFormatter.php"
-		]
 	}
 }
diff --git a/packages/js/e2e-core-tests/composer.json b/packages/js/e2e-core-tests/composer.json
index cf9c906db48..93e0c6ec09b 100644
--- a/packages/js/e2e-core-tests/composer.json
+++ b/packages/js/e2e-core-tests/composer.json
@@ -10,7 +10,7 @@
 	"extra": {
 		"changelogger": {
 			"formatter": {
-				"class": "PackageFormatter"
+				"filename": "../../../tools/changelogger/PackageFormatter.php"
 			},
 			"types": [
 				"Fix",
@@ -23,10 +23,5 @@
 			],
 			"changelog": "NEXT_CHANGELOG.md"
 		}
-	},
-	"autoload": {
-		"files": [
-			"../../../tools/changelogger/PackageFormatter.php"
-		]
 	}
 }
diff --git a/packages/js/e2e-environment/composer.json b/packages/js/e2e-environment/composer.json
index e050b6a4b24..9297a4b6592 100644
--- a/packages/js/e2e-environment/composer.json
+++ b/packages/js/e2e-environment/composer.json
@@ -10,7 +10,7 @@
 	"extra": {
 		"changelogger": {
 			"formatter": {
-				"class": "PackageFormatter"
+				"filename": "../../../tools/changelogger/PackageFormatter.php"
 			},
 			"types": [
 				"Fix",
@@ -23,10 +23,5 @@
 			],
 			"changelog": "NEXT_CHANGELOG.md"
 		}
-	},
-	"autoload": {
-		"files": [
-			"../../../tools/changelogger/PackageFormatter.php"
-		]
 	}
 }
diff --git a/packages/js/e2e-utils/composer.json b/packages/js/e2e-utils/composer.json
index ea5bf85684f..ef52c1b8559 100644
--- a/packages/js/e2e-utils/composer.json
+++ b/packages/js/e2e-utils/composer.json
@@ -10,7 +10,7 @@
 	"extra": {
 		"changelogger": {
 			"formatter": {
-				"class": "PackageFormatter"
+				"filename": "../../../tools/changelogger/PackageFormatter.php"
 			},
 			"types": [
 				"Fix",
@@ -23,10 +23,5 @@
 			],
 			"changelog": "NEXT_CHANGELOG.md"
 		}
-	},
-	"autoload": {
-		"files": [
-			"../../../tools/changelogger/PackageFormatter.php"
-		]
 	}
 }
diff --git a/plugins/woocommerce/bin/composer/mozart/composer.lock b/plugins/woocommerce/bin/composer/mozart/composer.lock
index 89a287c2370..ffc24351bb8 100644
--- a/plugins/woocommerce/bin/composer/mozart/composer.lock
+++ b/plugins/woocommerce/bin/composer/mozart/composer.lock
@@ -1153,5 +1153,5 @@
     "platform-overrides": {
         "php": "7.3"
     },
-    "plugin-api-version": "2.0.0"
+    "plugin-api-version": "2.1.0"
 }
diff --git a/plugins/woocommerce/bin/composer/phpcs/composer.lock b/plugins/woocommerce/bin/composer/phpcs/composer.lock
index 7ac437c734a..c672998035f 100644
--- a/plugins/woocommerce/bin/composer/phpcs/composer.lock
+++ b/plugins/woocommerce/bin/composer/phpcs/composer.lock
@@ -411,5 +411,5 @@
     "platform-overrides": {
         "php": "7.0"
     },
-    "plugin-api-version": "2.0.0"
+    "plugin-api-version": "2.1.0"
 }
diff --git a/plugins/woocommerce/bin/composer/phpunit/composer.lock b/plugins/woocommerce/bin/composer/phpunit/composer.lock
index e4f038f8f36..d6320b80455 100644
--- a/plugins/woocommerce/bin/composer/phpunit/composer.lock
+++ b/plugins/woocommerce/bin/composer/phpunit/composer.lock
@@ -1697,5 +1697,5 @@
     "platform-overrides": {
         "php": "7.0"
     },
-    "plugin-api-version": "2.0.0"
+    "plugin-api-version": "2.1.0"
 }
diff --git a/plugins/woocommerce/bin/composer/wp/composer.lock b/plugins/woocommerce/bin/composer/wp/composer.lock
index cf54f60f475..fb6330f9c9a 100644
--- a/plugins/woocommerce/bin/composer/wp/composer.lock
+++ b/plugins/woocommerce/bin/composer/wp/composer.lock
@@ -164,16 +164,16 @@
         },
         {
             "name": "mck89/peast",
-            "version": "v1.13.8",
+            "version": "v1.13.9",
             "source": {
                 "type": "git",
                 "url": "https://github.com/mck89/peast.git",
-                "reference": "4f0423441ec557f3935b056d10987f2e1c7a3e76"
+                "reference": "5329e997fb50e0b82ca8f6e4164f92941f689b47"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/mck89/peast/zipball/4f0423441ec557f3935b056d10987f2e1c7a3e76",
-                "reference": "4f0423441ec557f3935b056d10987f2e1c7a3e76",
+                "url": "https://api.github.com/repos/mck89/peast/zipball/5329e997fb50e0b82ca8f6e4164f92941f689b47",
+                "reference": "5329e997fb50e0b82ca8f6e4164f92941f689b47",
                 "shasum": ""
             },
             "require": {
@@ -185,7 +185,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "1.13.8-dev"
+                    "dev-master": "1.13.9-dev"
                 }
             },
             "autoload": {
@@ -207,9 +207,9 @@
             "description": "Peast is PHP library that generates AST for JavaScript code",
             "support": {
                 "issues": "https://github.com/mck89/peast/issues",
-                "source": "https://github.com/mck89/peast/tree/v1.13.8"
+                "source": "https://github.com/mck89/peast/tree/v1.13.9"
             },
-            "time": "2021-09-11T10:28:18+00:00"
+            "time": "2021-11-12T13:44:49+00:00"
         },
         {
             "name": "mustache/mustache",
@@ -624,5 +624,5 @@
     "platform-overrides": {
         "php": "7.0"
     },
-    "plugin-api-version": "2.0.0"
+    "plugin-api-version": "2.1.0"
 }
diff --git a/plugins/woocommerce/composer.json b/plugins/woocommerce/composer.json
index 2471c444ace..1d579936d2a 100644
--- a/plugins/woocommerce/composer.json
+++ b/plugins/woocommerce/composer.json
@@ -55,10 +55,7 @@
 		},
 		"psr-0": {
 			"Automattic\\WooCommerce\\Vendor\\": "lib/packages/"
-		},
-		"files": [
-			"../../tools/changelogger/PluginFormatter.php"
-		]
+		}
 	},
 	"autoload-dev": {
 		"psr-4": {
@@ -123,7 +120,7 @@
 		},
 		"changelogger": {
 			"formatter": {
-				"class": "PluginFormatter"
+				"filename": "../../tools/changelogger/PluginFormatter.php"
 			},
 			"types": [
 				"Fix",
diff --git a/plugins/woocommerce/composer.lock b/plugins/woocommerce/composer.lock
index 686e2011669..930a255ddce 100644
--- a/plugins/woocommerce/composer.lock
+++ b/plugins/woocommerce/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "8d115ec1c2d2dab03533d674edb48a44",
+    "content-hash": "f6fc527d8719df0b0247ee188eb3eee9",
     "packages": [
         {
             "name": "automattic/jetpack-autoloader",
@@ -2923,5 +2923,5 @@
     "platform-overrides": {
         "php": "7.0.33"
     },
-    "plugin-api-version": "2.0.0"
+    "plugin-api-version": "2.1.0"
 }
diff --git a/tools/changelogger/Formatter.php b/tools/changelogger/Formatter.php
index f9119c65a79..f24f63d007a 100644
--- a/tools/changelogger/Formatter.php
+++ b/tools/changelogger/Formatter.php
@@ -1,19 +1,24 @@
 <?php
+
+namespace Automattic\WooCommerce\MonorepoTools\Changelogger;
+
 /**
  * Base Jetpack Changelogger Formatter for WooCommerce
  */
 
 use Automattic\Jetpack\Changelog\Changelog;
 use Automattic\Jetpack\Changelog\KeepAChangelogParser;
-use Automattic\Jetpack\Changelogger\FormatterPlugin;
 use Automattic\Jetpack\Changelogger\PluginTrait;
 
 /**
  * Base Jetpack Changelogger Formatter for WooCommerce
  *
+ * Note: Since the "filename" loading relies on a single class implementing the plugin interface,
+ * we have to implement it in the child class, even though the base class satisfies it.
+ *
  * Class Formatter
  */
-class Formatter extends KeepAChangelogParser implements FormatterPlugin {
+class Formatter extends KeepAChangelogParser {
 	use PluginTrait;
 
 	/**
@@ -61,7 +66,7 @@ class Formatter extends KeepAChangelogParser implements FormatterPlugin {
 	/**
 	 * Get Release link given a version number.
 	 *
-	 * @throws InvalidArgumentException When directory parsing fails.
+	 * @throws \InvalidArgumentException When directory parsing fails.
 	 * @param string $version Release version.
 	 *
 	 * @return string Link to the version's release.
@@ -76,13 +81,13 @@ class Formatter extends KeepAChangelogParser implements FormatterPlugin {
 		preg_match( '/\/woocommerce\/(.+)/', getcwd(), $path );
 
 		if ( ! count( $path ) ) {
-			throw new InvalidArgumentException( 'Invalid directory.' );
+			throw new \InvalidArgumentException( 'Invalid directory.' );
 		}
 
 		$release_url = $path_map[ $path[1] ];
 
 		if ( ! $release_url ) {
-			throw new InvalidArgumentException( 'Release URL not found.' );
+			throw new \InvalidArgumentException( 'Release URL not found.' );
 		}
 
 		return $release_url . $version;
@@ -93,7 +98,7 @@ class Formatter extends KeepAChangelogParser implements FormatterPlugin {
 	 *
 	 * @param string $changelog Changelog contents.
 	 * @return Changelog
-	 * @throws InvalidArgumentException If the changelog data cannot be parsed.
+	 * @throws \InvalidArgumentException If the changelog data cannot be parsed.
 	 */
 	public function parse( $changelog ) {
 		$ret = new Changelog();
@@ -131,7 +136,7 @@ class Formatter extends KeepAChangelogParser implements FormatterPlugin {
 			$is_subentry = count( $subheading ) > 0;
 
 			if ( ! count( $heading ) && ! count( $subheading ) ) {
-				throw new InvalidArgumentException( 'Invalid heading' );
+				throw new \InvalidArgumentException( 'Invalid heading' );
 			}
 
 			$version         = '';
@@ -145,11 +150,11 @@ class Formatter extends KeepAChangelogParser implements FormatterPlugin {
 				try {
 					$timestamp = new DateTime( $timestamp, new DateTimeZone( 'UTC' ) );
 				} catch ( \Exception $ex ) {
-					throw new InvalidArgumentException( "Heading has an invalid timestamp: $heading", 0, $ex );
+					throw new \InvalidArgumentException( "Heading has an invalid timestamp: $heading", 0, $ex );
 				}
 
 				if ( strtotime( $heading[2], 0 ) !== strtotime( $heading[2], 1000000000 ) ) {
-					throw new InvalidArgumentException( "Heading has a relative timestamp: $heading" );
+					throw new \InvalidArgumentException( "Heading has a relative timestamp: $heading" );
 				}
 				$entry_timestamp = $timestamp;
 
@@ -271,4 +276,4 @@ class Formatter extends KeepAChangelogParser implements FormatterPlugin {
 
 		return $ret;
 	}
-} 
+}
diff --git a/tools/changelogger/PackageFormatter.php b/tools/changelogger/PackageFormatter.php
index 0d3000fe0ae..0763aedc631 100644
--- a/tools/changelogger/PackageFormatter.php
+++ b/tools/changelogger/PackageFormatter.php
@@ -1,4 +1,9 @@
 <?php
+
+namespace Automattic\WooCommerce\MonorepoTools\Changelogger;
+
+use Automattic\Jetpack\Changelogger\FormatterPlugin;
+
 /**
  * Jetpack Changelogger Formatter for WooCommerce packages
  */
@@ -10,7 +15,7 @@ require_once 'Formatter.php';
  *
  * Class Formatter
  */
-class PackageFormatter extends Formatter {
+class PackageFormatter extends Formatter implements FormatterPlugin {
 	/**
 	 * Prologue text.
 	 *
diff --git a/tools/changelogger/PluginFormatter.php b/tools/changelogger/PluginFormatter.php
index 620da70105c..20208075364 100644
--- a/tools/changelogger/PluginFormatter.php
+++ b/tools/changelogger/PluginFormatter.php
@@ -1,4 +1,9 @@
 <?php
+
+namespace Automattic\WooCommerce\MonorepoTools\Changelogger;
+
+use Automattic\Jetpack\Changelogger\FormatterPlugin;
+
 /**
  * Jetpack Changelogger Formatter for WooCommerce plugins
  */
@@ -10,7 +15,7 @@ require_once 'Formatter.php';
  *
  * Class Formatter
  */
-class PluginFormatter extends Formatter {
+class PluginFormatter extends Formatter implements FormatterPlugin {
 	/**
 	 * Epilogue text.
 	 *
@@ -24,4 +29,4 @@ class PluginFormatter extends Formatter {
 	 * @var string
 	 */
 	public $entry_pattern = '/^##?#\s+([^\n=]+)\s+((?:(?!^##).)+)/ms';
-} 
+}