diff --git a/libraries/joomla/event/dispatcher.php b/libraries/joomla/event/dispatcher.php
index b7248ddde8801..fb2c908a0fc8a 100644
--- a/libraries/joomla/event/dispatcher.php
+++ b/libraries/joomla/event/dispatcher.php
@@ -15,8 +15,9 @@
  * This is the Observable part of the Observer design pattern
  * for the event architecture.
  *
- * @see    JPlugin
- * @since  12.1
+ * @see         JPlugin
+ * @since       12.1
+ * @deprecated  4.0  The CMS' Event classes will be replaced with the `joomla/event` package
  */
 class JEventDispatcher extends JObject
 {
diff --git a/libraries/joomla/event/event.php b/libraries/joomla/event/event.php
index 82a8dca966ed7..f3d1f3ecb85ea 100644
--- a/libraries/joomla/event/event.php
+++ b/libraries/joomla/event/event.php
@@ -12,7 +12,8 @@
 /**
  * JEvent Class
  *
- * @since  11.1
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Event classes will be replaced with the `joomla/event` package
  */
 abstract class JEvent extends JObject
 {
diff --git a/libraries/joomla/session/exception/unsupported.php b/libraries/joomla/session/exception/unsupported.php
index 87285eec72d38..2284613009bd2 100644
--- a/libraries/joomla/session/exception/unsupported.php
+++ b/libraries/joomla/session/exception/unsupported.php
@@ -12,7 +12,8 @@
 /**
  * Exception class defining an unsupported session storage object
  *
- * @since  3.6.3
+ * @since       3.6.3
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionExceptionUnsupported extends RuntimeException
 {
diff --git a/libraries/joomla/session/handler/interface.php b/libraries/joomla/session/handler/interface.php
index c7a7faedd9037..609c7b0d073cc 100644
--- a/libraries/joomla/session/handler/interface.php
+++ b/libraries/joomla/session/handler/interface.php
@@ -12,7 +12,8 @@
 /**
  * Interface for managing HTTP sessions
  *
- * @since  3.5
+ * @since       3.5
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 interface JSessionHandlerInterface
 {
diff --git a/libraries/joomla/session/handler/joomla.php b/libraries/joomla/session/handler/joomla.php
index 7d3c97bfcd026..f93f9ba588146 100644
--- a/libraries/joomla/session/handler/joomla.php
+++ b/libraries/joomla/session/handler/joomla.php
@@ -12,7 +12,8 @@
 /**
  * Interface for managing HTTP sessions
  *
- * @since  3.5
+ * @since       3.5
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionHandlerJoomla extends JSessionHandlerNative
 {
diff --git a/libraries/joomla/session/handler/native.php b/libraries/joomla/session/handler/native.php
index 8ad389fa148c6..59372a2b78ee4 100644
--- a/libraries/joomla/session/handler/native.php
+++ b/libraries/joomla/session/handler/native.php
@@ -12,7 +12,8 @@
 /**
  * Interface for managing HTTP sessions
  *
- * @since  3.5
+ * @since       3.5
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionHandlerNative implements JSessionHandlerInterface
 {
diff --git a/libraries/joomla/session/storage.php b/libraries/joomla/session/storage.php
index a756be7efa42e..1ad47bd9774dd 100644
--- a/libraries/joomla/session/storage.php
+++ b/libraries/joomla/session/storage.php
@@ -12,9 +12,9 @@
 /**
  * Custom session storage handler for PHP
  *
- * @see    https://secure.php.net/manual/en/function.session-set-save-handler.php
- * @todo   When dropping compatibility with PHP 5.3 use the SessionHandlerInterface and the SessionHandler class
- * @since  11.1
+ * @see         https://secure.php.net/manual/en/function.session-set-save-handler.php
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 abstract class JSessionStorage
 {
diff --git a/libraries/joomla/session/storage/apc.php b/libraries/joomla/session/storage/apc.php
index d530d9866ca2a..45350b7046775 100644
--- a/libraries/joomla/session/storage/apc.php
+++ b/libraries/joomla/session/storage/apc.php
@@ -12,8 +12,9 @@
 /**
  * APC session storage handler for PHP
  *
- * @see    https://secure.php.net/manual/en/function.session-set-save-handler.php
- * @since  11.1
+ * @see         https://secure.php.net/manual/en/function.session-set-save-handler.php
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionStorageApc extends JSessionStorage
 {
diff --git a/libraries/joomla/session/storage/database.php b/libraries/joomla/session/storage/database.php
index 2f1f05e40042e..da7b242cf388d 100644
--- a/libraries/joomla/session/storage/database.php
+++ b/libraries/joomla/session/storage/database.php
@@ -12,8 +12,9 @@
 /**
  * Database session storage handler for PHP
  *
- * @see    https://secure.php.net/manual/en/function.session-set-save-handler.php
- * @since  11.1
+ * @see         https://secure.php.net/manual/en/function.session-set-save-handler.php
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionStorageDatabase extends JSessionStorage
 {
diff --git a/libraries/joomla/session/storage/memcache.php b/libraries/joomla/session/storage/memcache.php
index d5f6fbb417958..896429abc1591 100644
--- a/libraries/joomla/session/storage/memcache.php
+++ b/libraries/joomla/session/storage/memcache.php
@@ -12,7 +12,8 @@
 /**
  * Memcache session storage handler for PHP
  *
- * @since  11.1
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionStorageMemcache extends JSessionStorage
 {
diff --git a/libraries/joomla/session/storage/memcached.php b/libraries/joomla/session/storage/memcached.php
index fb536b4a124da..06576ef528549 100644
--- a/libraries/joomla/session/storage/memcached.php
+++ b/libraries/joomla/session/storage/memcached.php
@@ -12,7 +12,8 @@
 /**
  * Memcached session storage handler for PHP
  *
- * @since  11.1
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionStorageMemcached extends JSessionStorage
 {
diff --git a/libraries/joomla/session/storage/none.php b/libraries/joomla/session/storage/none.php
index ab7e84bb85af5..60aaccf5baaa3 100644
--- a/libraries/joomla/session/storage/none.php
+++ b/libraries/joomla/session/storage/none.php
@@ -12,8 +12,9 @@
 /**
  * File session handler for PHP
  *
- * @see    https://secure.php.net/manual/en/function.session-set-save-handler.php
- * @since  11.1
+ * @see         https://secure.php.net/manual/en/function.session-set-save-handler.php
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionStorageNone extends JSessionStorage
 {
diff --git a/libraries/joomla/session/storage/wincache.php b/libraries/joomla/session/storage/wincache.php
index afee067fc9866..ac785bf1f1cf2 100644
--- a/libraries/joomla/session/storage/wincache.php
+++ b/libraries/joomla/session/storage/wincache.php
@@ -12,7 +12,8 @@
 /**
  * WINCACHE session storage handler for PHP
  *
- * @since  11.1
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionStorageWincache extends JSessionStorage
 {
diff --git a/libraries/joomla/session/storage/xcache.php b/libraries/joomla/session/storage/xcache.php
index 1afd5120dde9e..e33fc0a2bda05 100644
--- a/libraries/joomla/session/storage/xcache.php
+++ b/libraries/joomla/session/storage/xcache.php
@@ -12,7 +12,8 @@
 /**
  * XCache session storage handler
  *
- * @since  11.1
+ * @since       11.1
+ * @deprecated  4.0  The CMS' Session classes will be replaced with the `joomla/session` package
  */
 class JSessionStorageXcache extends JSessionStorage
 {