diff --git a/PicoDeprecated.php b/PicoDeprecated.php
index a053bf7..6ed7d02 100644
--- a/PicoDeprecated.php
+++ b/PicoDeprecated.php
@@ -46,7 +46,7 @@ class PicoDeprecated extends AbstractPicoPlugin
      *
      * @var int
      */
-    public const API_VERSION = 3;
+    public const API_VERSION = 4;
 
     /**
      * API version 0, used by Pico 0.9 and earlier
@@ -76,6 +76,13 @@ class PicoDeprecated extends AbstractPicoPlugin
      */
     public const API_VERSION_3 = 3;
 
+    /**
+     * API version 4, used by Pico 3.0
+     *
+     * @var int
+     */
+    public const API_VERSION_4 = 4;
+
     /**
      * Loaded plugins, indexed by API version
      *
diff --git a/plugins/PluginApi3Plugin.php b/plugins/PluginApi3Plugin.php
new file mode 100644
index 0000000..ebaa1c9
--- /dev/null
+++ b/plugins/PluginApi3Plugin.php
@@ -0,0 +1,91 @@
+<?php
+/**
+ * This file is part of Pico. It's copyrighted by the contributors recorded
+ * in the version control history of the file, available from the following
+ * original location:
+ *
+ * <https://github.com/picocms/pico-deprecated/blob/master/plugins/PluginApi3Plugin.php>
+ *
+ * SPDX-License-Identifier: MIT
+ * License-Filename: LICENSE
+ */
+
+namespace picocms\PicoDeprecated\Plugin;
+
+use picocms\PicoDeprecated\AbstractPluginApiPlugin;
+use PicoDeprecated;
+
+/**
+ * Maintains backward compatibility with plugins using API version 3, written
+ * for Pico 2.1
+ *
+ * @author  Daniel Rudolf
+ * @link    http://picocms.org
+ * @license http://opensource.org/licenses/MIT The MIT License
+ * @version 3.0
+ */
+class PluginApi3Plugin extends AbstractPluginApiPlugin
+{
+    /**
+     * This plugin extends {@see ThemeApi3Plugin}
+     *
+     * @var string[]
+     */
+    protected $dependsOn = [ ThemeApi3Plugin::class ];
+
+    /**
+     * Map of core events matching event signatures of older API versions
+     *
+     * @see AbstractPluginApiPlugin::handleEvent()
+     *
+     * @var array<string,string>
+     */
+    protected $eventAliases = [
+        'onPluginsLoaded' =>         [ 'onPluginsLoaded' ],
+        'onPluginManuallyLoaded' =>  [ 'onPluginManuallyLoaded' ],
+        'onConfigLoaded' =>          [ 'onConfigLoaded' ],
+        'onThemeLoading' =>          [ 'onThemeLoading' ],
+        'onThemeLoaded' =>           [ 'onThemeLoaded' ],
+        'onRequestUrl' =>            [ 'onRequestUrl' ],
+        'onRequestFile' =>           [ 'onRequestFile' ],
+        'onContentLoading' =>        [ 'onContentLoading' ],
+        'on404ContentLoading' =>     [ 'on404ContentLoading' ],
+        'on404ContentLoaded' =>      [ 'on404ContentLoaded' ],
+        'onContentLoaded' =>         [ 'onContentLoaded' ],
+        'onMetaParsing' =>           [ 'onMetaParsing' ],
+        'onMetaParsed' =>            [ 'onMetaParsed' ],
+        'onContentParsing' =>        [ 'onContentParsing' ],
+        'onContentPrepared' =>       [ 'onContentPrepared' ],
+        'onContentParsed' =>         [ 'onContentParsed' ],
+        'onPagesLoading' =>          [ 'onPagesLoading' ],
+        'onSinglePageLoading' =>     [ 'onSinglePageLoading' ],
+        'onSinglePageContent' =>     [ 'onSinglePageContent' ],
+        'onSinglePageLoaded' =>      [ 'onSinglePageLoaded' ],
+        'onPagesDiscovered' =>       [ 'onPagesDiscovered' ],
+        'onPagesLoaded' =>           [ 'onPagesLoaded' ],
+        'onCurrentPageDiscovered' => [ 'onCurrentPageDiscovered' ],
+        'onPageTreeBuilt' =>         [ 'onPageTreeBuilt' ],
+        'onPageRendering' =>         [ 'onPageRendering' ],
+        'onPageRendered' =>          [ 'onPageRendered' ],
+        'onMetaHeaders' =>           [ 'onMetaHeaders' ],
+        'onYamlParserRegistered' =>  [ 'onYamlParserRegistered' ],
+        'onParsedownRegistered' =>   [ 'onParsedownRegistered' ],
+        'onTwigRegistered' =>        [ 'onTwigRegistered' ],
+    ];
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getApiVersion()
+    {
+        return PicoDeprecated::API_VERSION_4;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getApiVersionSupport()
+    {
+        return PicoDeprecated::API_VERSION_3;
+    }
+}
diff --git a/plugins/ThemeApi3Plugin.php b/plugins/ThemeApi3Plugin.php
new file mode 100644
index 0000000..5cbdce3
--- /dev/null
+++ b/plugins/ThemeApi3Plugin.php
@@ -0,0 +1,36 @@
+<?php
+/**
+ * This file is part of Pico. It's copyrighted by the contributors recorded
+ * in the version control history of the file, available from the following
+ * original location:
+ *
+ * <https://github.com/picocms/pico-deprecated/blob/master/plugins/ThemeApi3Plugin.php>
+ *
+ * SPDX-License-Identifier: MIT
+ * License-Filename: LICENSE
+ */
+
+namespace picocms\PicoDeprecated\Plugin;
+
+use picocms\PicoDeprecated\AbstractPlugin;
+use PicoDeprecated;
+
+/**
+ * Maintains backward compatibility with themes using API version 3, written
+ * for Pico 2.1
+ *
+ * @author  Daniel Rudolf
+ * @link    http://picocms.org
+ * @license http://opensource.org/licenses/MIT The MIT License
+ * @version 3.0
+ */
+class ThemeApi3Plugin extends AbstractPlugin
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function getApiVersion()
+    {
+        return PicoDeprecated::API_VERSION_4;
+    }
+}