diff --git a/CHANGELOG b/CHANGELOG
index a29d4019e..ee6f4d87a 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,6 @@
 # 3.12.0 (2024-XX-XX)
 
+ * Deprecate the `spaceless` filter
  * Deprecate some internal methods from `Parser`: `getBlockStack()`, `hasBlock()`, `getBlock()`, `hasMacro()`, `hasTraits()`, `getParent()`
  * Deprecate passing `null` to `Twig\Parser::setParent()`
  * Update `Node::__toString()` to include the node tag if set
diff --git a/doc/deprecated.rst b/doc/deprecated.rst
index 83a33a537..950d961dd 100644
--- a/doc/deprecated.rst
+++ b/doc/deprecated.rst
@@ -180,3 +180,9 @@ Templates
   in ``Environment::resolveTemplate()``, ``Environment::load()``, and
   ``Template::loadTemplate()``); pass instances of ``Twig\TemplateWrapper``
   instead.
+
+Filters
+-------
+
+* The ``spaceless`` filter is deprecated as of Twig 3.12 and will be removed in
+  Twig 4.0.
diff --git a/doc/filters/spaceless.rst b/doc/filters/spaceless.rst
index 9a213c370..7a8e4093e 100644
--- a/doc/filters/spaceless.rst
+++ b/doc/filters/spaceless.rst
@@ -1,6 +1,10 @@
 ``spaceless``
 =============
 
+.. warning::
+
+    The ``spaceless`` filter is deprecated as of Twig 3.12.
+
 Use the ``spaceless`` filter to remove whitespace *between HTML tags*, not
 whitespace within HTML tags or whitespace in plain text:
 
diff --git a/src/Extension/CoreExtension.php b/src/Extension/CoreExtension.php
index cd2f5d7e6..14dde136a 100644
--- a/src/Extension/CoreExtension.php
+++ b/src/Extension/CoreExtension.php
@@ -215,7 +215,7 @@ final class CoreExtension extends AbstractExtension
             new TwigFilter('striptags', [self::class, 'striptags']),
             new TwigFilter('trim', [self::class, 'trim']),
             new TwigFilter('nl2br', [self::class, 'nl2br'], ['pre_escape' => 'html', 'is_safe' => ['html']]),
-            new TwigFilter('spaceless', [self::class, 'spaceless'], ['is_safe' => ['html']]),
+            new TwigFilter('spaceless', [self::class, 'spaceless'], ['is_safe' => ['html'], 'deprecated' => '3.12', 'deprecating_package' => 'twig/twig']),
 
             // array helpers
             new TwigFilter('join', [self::class, 'join']),
diff --git a/tests/Fixtures/filters/spaceless.legacy.test b/tests/Fixtures/filters/spaceless.legacy.test
new file mode 100644
index 000000000..6a01241e7
--- /dev/null
+++ b/tests/Fixtures/filters/spaceless.legacy.test
@@ -0,0 +1,16 @@
+--TEST--
+"spaceless" filter
+--DEPRECATION--
+Since twig/twig 3.12: Twig Filter "spaceless" is deprecated in index.twig at line 2.
+Since twig/twig 3.12: Twig Filter "spaceless" is deprecated in index.twig at line 3.
+Since twig/twig 3.12: Twig Filter "spaceless" is deprecated in index.twig at line 4.
+--TEMPLATE--
+{{ "    <div>   <div>   foo   </div>   </div>"|spaceless }}
+*{{ ""|spaceless }}*
+*{{ null|spaceless }}*
+--DATA--
+return []
+--EXPECT--
+<div><div>   foo   </div></div>
+**
+**
diff --git a/tests/Fixtures/filters/spaceless.test b/tests/Fixtures/filters/spaceless.test
deleted file mode 100644
index 166a7ea0b..000000000
--- a/tests/Fixtures/filters/spaceless.test
+++ /dev/null
@@ -1,12 +0,0 @@
---TEST--
-"spaceless" filter
---TEMPLATE--
-{{ "    <div>   <div>   foo   </div>   </div>"|spaceless }}
-*{{ ""|spaceless }}*
-*{{ null|spaceless }}*
---DATA--
-return []
---EXPECT--
-<div><div>   foo   </div></div>
-**
-**
diff --git a/tests/Fixtures/macros/macro_with_capture.test b/tests/Fixtures/macros/macro_with_capture.test
index f67a7fcdb..2f9caed6e 100644
--- a/tests/Fixtures/macros/macro_with_capture.test
+++ b/tests/Fixtures/macros/macro_with_capture.test
@@ -4,11 +4,11 @@ macro
 {{ _self.some_macro() }}
 
 {% macro some_macro() %}
-    {% apply spaceless %}
+    {% apply upper %}
         {% if true %}foo{% endif %}
     {% endapply %}
 {% endmacro %}
 --DATA--
 return []
 --EXPECT--
-foo
+FOO
diff --git a/tests/Fixtures/tags/apply/scope.test b/tests/Fixtures/tags/apply/scope.test
index a87ff9116..ff8a23116 100644
--- a/tests/Fixtures/tags/apply/scope.test
+++ b/tests/Fixtures/tags/apply/scope.test
@@ -2,7 +2,7 @@
 "apply" tag does not create a new scope
 --TEMPLATE--
 {% set foo = 'baz' %}
-{% apply spaceless %}
+{% apply upper %}
     {% set foo = 'foo' %}
     {% set bar = 'bar' %}
 {% endapply %}