diff --git a/UPGRADE-5.0.md b/UPGRADE-5.0.md
index 74c8bd4580..e6222abe89 100644
--- a/UPGRADE-5.0.md
+++ b/UPGRADE-5.0.md
@@ -382,6 +382,7 @@ SecurityBundle
 Serializer
 ----------
 
+ * The default value of the `CsvEncoder` "as_collection" option was changed to `true`.
  * The `AbstractNormalizer::handleCircularReference()` method has two new `$format` and `$context` arguments.
 
 Translation
diff --git a/src/Symfony/Component/Serializer/CHANGELOG.md b/src/Symfony/Component/Serializer/CHANGELOG.md
index 9cdb2243be..4b05d8af94 100644
--- a/src/Symfony/Component/Serializer/CHANGELOG.md
+++ b/src/Symfony/Component/Serializer/CHANGELOG.md
@@ -6,6 +6,7 @@ CHANGELOG
 
  * throw an exception when creating a `Serializer` with normalizers which neither implement `NormalizerInterface` nor `DenormalizerInterface`
  * throw an exception when creating a `Serializer` with encoders which neither implement `EncoderInterface` nor `DecoderInterface`
+ * changed the default value of the `CsvEncoder` "as_collection" option to `true`
 
 4.3.0
 -----
diff --git a/src/Symfony/Component/Serializer/Encoder/CsvEncoder.php b/src/Symfony/Component/Serializer/Encoder/CsvEncoder.php
index 123ecf7dd1..c35107d583 100644
--- a/src/Symfony/Component/Serializer/Encoder/CsvEncoder.php
+++ b/src/Symfony/Component/Serializer/Encoder/CsvEncoder.php
@@ -33,6 +33,7 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
 
     private $formulasStartCharacters = ['=', '-', '+', '@'];
     private $defaultContext = [
+        self::AS_COLLECTION_KEY => true,
         self::DELIMITER_KEY => ',',
         self::ENCLOSURE_KEY => '"',
         self::ESCAPE_CHAR_KEY => '\\',
@@ -135,7 +136,7 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
         $headerCount = [];
         $result = [];
 
-        list($delimiter, $enclosure, $escapeChar, $keySeparator) = $this->getCsvOptions($context);
+        list($delimiter, $enclosure, $escapeChar, $keySeparator, , , $asCollection) = $this->getCsvOptions($context);
 
         while (false !== ($cols = fgetcsv($handle, 0, $delimiter, $enclosure, $escapeChar))) {
             $nbCols = \count($cols);
@@ -183,7 +184,7 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
         }
         fclose($handle);
 
-        if ($context[self::AS_COLLECTION_KEY] ?? false) {
+        if ($asCollection) {
             return $result;
         }
 
@@ -191,10 +192,6 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
             return $result;
         }
 
-        if (!isset($context['as_collection'])) {
-            @trigger_error('Relying on the default value (false) of the "as_collection" option is deprecated since 4.2. You should set it to false explicitly instead as true will be the default value in 5.0.', E_USER_DEPRECATED);
-        }
-
         // If there is only one data line in the document, return it (the line), the result is not considered as a collection
         return $result[0];
     }
@@ -233,12 +230,13 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
         $keySeparator = $context[self::KEY_SEPARATOR_KEY] ?? $this->defaultContext[self::KEY_SEPARATOR_KEY];
         $headers = $context[self::HEADERS_KEY] ?? $this->defaultContext[self::HEADERS_KEY];
         $escapeFormulas = $context[self::ESCAPE_FORMULAS_KEY] ?? $this->defaultContext[self::ESCAPE_FORMULAS_KEY];
+        $asCollection = $context[self::AS_COLLECTION_KEY] ?? $this->defaultContext[self::AS_COLLECTION_KEY];
 
         if (!\is_array($headers)) {
             throw new InvalidArgumentException(sprintf('The "%s" context variable must be an array or null, given "%s".', self::HEADERS_KEY, \gettype($headers)));
         }
 
-        return [$delimiter, $enclosure, $escapeChar, $keySeparator, $headers, $escapeFormulas];
+        return [$delimiter, $enclosure, $escapeChar, $keySeparator, $headers, $escapeFormulas, $asCollection];
     }
 
     /**
diff --git a/src/Symfony/Component/Serializer/Tests/Encoder/CsvEncoderTest.php b/src/Symfony/Component/Serializer/Tests/Encoder/CsvEncoderTest.php
index 74235c46c1..52c4a9b5c4 100644
--- a/src/Symfony/Component/Serializer/Tests/Encoder/CsvEncoderTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Encoder/CsvEncoderTest.php
@@ -327,21 +327,6 @@ CSV
         $this->assertFalse($this->encoder->supportsDecoding('foo'));
     }
 
-    /**
-     * @group legacy
-     * @expectedDeprecation Relying on the default value (false) of the "as_collection" option is deprecated since 4.2. You should set it to false explicitly instead as true will be the default value in 5.0.
-     */
-    public function testDecodeLegacy()
-    {
-        $expected = ['foo' => 'a', 'bar' => 'b'];
-
-        $this->assertEquals($expected, $this->encoder->decode(<<<'CSV'
-foo,bar
-a,b
-CSV
-        , 'csv'));
-    }
-
     public function testDecodeAsSingle()
     {
         $expected = ['foo' => 'a', 'bar' => 'b'];
@@ -382,9 +367,7 @@ foo
 a
 
 CSV
-        , 'csv', [
-            CsvEncoder::AS_COLLECTION_KEY => true, // Can be removed in 5.0
-        ]));
+        , 'csv'));
     }
 
     public function testDecodeToManyRelation()
@@ -449,9 +432,7 @@ CSV
 a;bar-baz
 'hell''o';b;c
 CSV
-        , 'csv', [
-            CsvEncoder::AS_COLLECTION_KEY => true, // Can be removed in 5.0
-        ]));
+        , 'csv'));
     }
 
     public function testDecodeCustomSettingsPassedInContext()
@@ -466,7 +447,6 @@ CSV
             CsvEncoder::ENCLOSURE_KEY => "'",
             CsvEncoder::ESCAPE_CHAR_KEY => '|',
             CsvEncoder::KEY_SEPARATOR_KEY => '-',
-            CsvEncoder::AS_COLLECTION_KEY => true, // Can be removed in 5.0
         ]));
     }