diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 88bc299..0e239b7 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -49,6 +49,17 @@ function file_help($route_name, RouteMatchInterface $route_match) {
 }
 
 /**
+ * Implements hook_field_widget_info_alter().
+ */
+function file_field_widget_info_alter(array &$info) {
+  // This allows setting a valid default widget in the FileUriItem annotation.
+  // It's not strictly needed, but it's a required value on the annotation so
+  // should be a valid value.
+  // @see \Drupal\file\Plugin\Field\FieldType\FileUriItem
+  $info['uri']['field_types'][] = 'file_uri';
+}
+
+/**
  * Loads file entities from the database.
  *
  * @param array|null $fids
diff --git a/core/modules/file/src/ComputedFileUrl.php b/core/modules/file/src/ComputedFileUrl.php
new file mode 100644
index 0000000..2eb012e
--- /dev/null
+++ b/core/modules/file/src/ComputedFileUrl.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\file;
+
+use Drupal\Core\TypedData\TypedData;
+
+/**
+ * Computed file URL property class.
+ */
+class ComputedFileUrl extends TypedData {
+
+  /**
+   * Computed root-relative file URL.
+   *
+   * @var string
+   */
+  protected $url = NULL;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getValue() {
+    if ($this->url !== NULL) {
+      return $this->url;
+    }
+
+    assert($this->getParent()->getEntity() instanceof FileInterface);
+
+    $uri = $this->getParent()->getEntity()->getFileUri();
+    $this->url = file_url_transform_relative(file_create_url($uri));
+
+    return $this->url;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setValue($value, $notify = TRUE) {
+    $this->url = $value;
+
+    // Notify the parent of any changes.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+  }
+
+}
diff --git a/core/modules/file/src/Entity/File.php b/core/modules/file/src/Entity/File.php
index a9ade9e..4060b77 100644
--- a/core/modules/file/src/Entity/File.php
+++ b/core/modules/file/src/Entity/File.php
@@ -243,7 +243,7 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
       ->setLabel(t('Filename'))
       ->setDescription(t('Name of the file with no path components.'));
 
-    $fields['uri'] = BaseFieldDefinition::create('uri')
+    $fields['uri'] = BaseFieldDefinition::create('file_uri')
       ->setLabel(t('URI'))
       ->setDescription(t('The URI to access the file (either local or remote).'))
       ->setSetting('max_length', 255)
diff --git a/core/modules/file/src/Plugin/Field/FieldFormatter/FileUriFormatter.php b/core/modules/file/src/Plugin/Field/FieldFormatter/FileUriFormatter.php
index 055e32d..0facb7e 100644
--- a/core/modules/file/src/Plugin/Field/FieldFormatter/FileUriFormatter.php
+++ b/core/modules/file/src/Plugin/Field/FieldFormatter/FileUriFormatter.php
@@ -13,7 +13,8 @@
  *   id = "file_uri",
  *   label = @Translation("File URI"),
  *   field_types = {
- *     "uri"
+ *     "uri",
+ *     "file_uri",
  *   }
  * )
  */
diff --git a/core/modules/file/src/Plugin/Field/FieldType/FileUriItem.php b/core/modules/file/src/Plugin/Field/FieldType/FileUriItem.php
new file mode 100644
index 0000000..84f0940
--- /dev/null
+++ b/core/modules/file/src/Plugin/Field/FieldType/FileUriItem.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\file\Plugin\Field\FieldType;
+
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\Core\Field\Plugin\Field\FieldType\UriItem;
+use Drupal\Core\TypedData\DataDefinition;
+use Drupal\file\ComputedFileUrl;
+
+/**
+ * File-specific plugin implementation of a URI item to provide a full URL.
+ *
+ * @FieldType(
+ *   id = "file_uri",
+ *   label = @Translation("File URI"),
+ *   description = @Translation("An entity field containing a file URI, and a computed root-relative file URL."),
+ *   no_ui = TRUE,
+ *   default_formatter = "file_uri",
+ *   default_widget = "uri",
+ * )
+ */
+class FileUriItem extends UriItem {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
+    $properties = parent::propertyDefinitions($field_definition);
+
+    $properties['url'] = DataDefinition::create('uri')
+      ->setLabel(t('Root-relative file URL'))
+      ->setSetting('case_sensitive', $field_definition->getSetting('case_sensitive'))
+      ->setComputed(TRUE)
+      ->setInternal(FALSE)
+      ->setClass(ComputedFileUrl::class);
+
+    return $properties;
+  }
+
+}
diff --git a/core/modules/file/tests/src/Kernel/FileUriItemTest.php b/core/modules/file/tests/src/Kernel/FileUriItemTest.php
new file mode 100644
index 0000000..d67eba0
--- /dev/null
+++ b/core/modules/file/tests/src/Kernel/FileUriItemTest.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\Tests\file\Kernel;
+
+use Drupal\file\Entity\File;
+
+/**
+ * File URI field item test.
+ *
+ * @group file
+ *
+ * @see \Drupal\file\Plugin\Field\FieldType\FileUriItem
+ * @see \Drupal\file\FileUrl
+ */
+class FileUriItemTest extends FileManagedUnitTestBase {
+
+  /**
+   * Tests the file entity override of the URI field.
+   */
+  public function testCustomFileUriField() {
+    $uri = 'public://druplicon.txt';
+
+    // Create a new file entity.
+    $file = File::create([
+      'uid' => 1,
+      'filename' => 'druplicon.txt',
+      'uri' => $uri,
+      'filemime' => 'text/plain',
+      'status' => FILE_STATUS_PERMANENT,
+    ]);
+    file_put_contents($file->getFileUri(), 'hello world');
+
+    $file->save();
+
+    $this->assertSame($uri, $file->uri->value);
+    $expected_url = base_path() . $this->siteDirectory . '/files/druplicon.txt';
+    $this->assertSame($expected_url, $file->uri->url);
+  }
+
+}
diff --git a/core/modules/file/tests/src/Unit/ComputedFileUrlTest.php b/core/modules/file/tests/src/Unit/ComputedFileUrlTest.php
new file mode 100644
index 0000000..8e2a4a4
--- /dev/null
+++ b/core/modules/file/tests/src/Unit/ComputedFileUrlTest.php
@@ -0,0 +1,91 @@
+<?php
+
+namespace Drupal\Tests\file\Unit;
+
+use Drupal\Core\Field\FieldItemInterface;
+use Drupal\Core\TypedData\DataDefinitionInterface;
+use Drupal\file\FileInterface;
+use Drupal\file\ComputedFileUrl;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @coversDefaultClass \Drupal\file\ComputedFileUrl
+ *
+ * @group file
+ */
+class ComputedFileUrlTest extends KernelTestBase {
+
+  /**
+   * The test URL to use.
+   *
+   * @var string
+   */
+  protected $testUrl = 'public://druplicon.txt';
+
+  /**
+   * @covers ::getValue
+   */
+  public function testGetValue() {
+    $entity = $this->prophesize(FileInterface::class);
+    $entity->getFileUri()
+      ->willReturn($this->testUrl);
+
+    $parent = $this->prophesize(FieldItemInterface::class);
+    $parent->getEntity()
+      ->shouldBeCalledTimes(2)
+      ->willReturn($entity->reveal());
+
+    $definition = $this->prophesize(DataDefinitionInterface::class);
+
+    $typed_data = new ComputedFileUrl($definition->reveal(), $this->randomMachineName(), $parent->reveal());
+
+    $expected = base_path() . $this->siteDirectory . '/files/druplicon.txt';
+
+    $this->assertSame($expected, $typed_data->getValue());
+    // Do this a second time to confirm the same value is returned but the value
+    // isn't retrieved from the parent entity again.
+    $this->assertSame($expected, $typed_data->getValue());
+  }
+
+  /**
+   * @covers ::setValue
+   */
+  public function testSetValue() {
+    $name = $this->randomMachineName();
+    $parent = $this->prophesize(FieldItemInterface::class);
+    $parent->onChange($name)
+      ->shouldBeCalled();
+
+    $definition = $this->prophesize(DataDefinitionInterface::class);
+    $typed_data = new ComputedFileUrl($definition->reveal(), $name, $parent->reveal());
+
+    // Setting the value explicitly should mean the parent entity is never
+    // called into.
+    $typed_data->setValue($this->testUrl);
+
+    $this->assertSame($this->testUrl, $typed_data->getValue());
+    // Do this a second time to confirm the same value is returned but the value
+    // isn't retrieved from the parent entity again.
+    $this->assertSame($this->testUrl, $typed_data->getValue());
+  }
+
+  /**
+   * @covers ::setValue
+   */
+  public function testSetValueNoNotify() {
+    $name = $this->randomMachineName();
+    $parent = $this->prophesize(FieldItemInterface::class);
+    $parent->onChange($name)
+      ->shouldNotBeCalled();
+
+    $definition = $this->prophesize(DataDefinitionInterface::class);
+    $typed_data = new ComputedFileUrl($definition->reveal(), $name, $parent->reveal());
+
+    // Setting the value should explicitly should mean the parent entity is
+    // never called into.
+    $typed_data->setValue($this->testUrl, FALSE);
+
+    $this->assertSame($this->testUrl, $typed_data->getValue());
+  }
+
+}
diff --git a/core/modules/hal/config/install/hal.settings.yml b/core/modules/hal/config/install/hal.settings.yml
index 67107af..1c895c1 100644
--- a/core/modules/hal/config/install/hal.settings.yml
+++ b/core/modules/hal/config/install/hal.settings.yml
@@ -1,3 +1,4 @@
 # Set the domain for HAL type and relation links.
 # If left blank, the site's domain will be used.
 link_domain: ~
+bc_file_uri_as_url_normalizer: false
diff --git a/core/modules/hal/config/schema/hal.schema.yml b/core/modules/hal/config/schema/hal.schema.yml
index 3192d67..b70f47e 100644
--- a/core/modules/hal/config/schema/hal.schema.yml
+++ b/core/modules/hal/config/schema/hal.schema.yml
@@ -6,3 +6,6 @@ hal.settings:
     link_domain:
       type: string
       label: 'Domain of the relation'
+    bc_file_uri_as_url_normalizer:
+      type: boolean
+      label: 'Whether to retain pre Drupal 8.5 behavior of normalizing file URI values as a full URL.'
diff --git a/core/modules/hal/hal.install b/core/modules/hal/hal.install
index 78810e3..0dc3fd5 100644
--- a/core/modules/hal/hal.install
+++ b/core/modules/hal/hal.install
@@ -31,3 +31,15 @@ function hal_update_8301() {
   $hal_settings->set('link_domain', $link_domain);
   $hal_settings->save(TRUE);
 }
+
+/**
+ * Add hal.settings::bc_file_uri_as_url_normalizer configuration.
+ */
+function hal_update_8501() {
+  $config_factory = \Drupal::configFactory();
+  $config_factory->getEditable('hal.settings')
+    ->set('bc_file_uri_as_url_normalizer', TRUE)
+    ->save(TRUE);
+
+  return t('The REST API will no longer return the full URL for file entity URI values for HAL+JSON responses. It will return the URI value itself, with an additional URL property providing a root relative file path. If your site depends on these value being strings, <a href="https://www.drupal.org/node/2925783">read the change record to learn how to enable the BC mode.</a>');
+}
diff --git a/core/modules/hal/hal.services.yml b/core/modules/hal/hal.services.yml
index b2c898f..a877163 100644
--- a/core/modules/hal/hal.services.yml
+++ b/core/modules/hal/hal.services.yml
@@ -14,9 +14,10 @@ services:
       - { name: normalizer, priority: 10 }
   serializer.normalizer.file_entity.hal:
     class: Drupal\hal\Normalizer\FileEntityNormalizer
+    deprecated: 'The "%service_id%" normalizer service is deprecated: it is obsolete, it only remains available for backwards compatibility.'
+    arguments: ['@entity.manager', '@http_client', '@hal.link_manager', '@module_handler', '@config.factory']
     tags:
       - { name: normalizer, priority: 20 }
-    arguments: ['@entity.manager', '@http_client', '@hal.link_manager', '@module_handler']
   serializer.normalizer.timestamp_item.hal:
    class: Drupal\hal\Normalizer\TimestampItemNormalizer
    tags:
diff --git a/core/modules/hal/src/Normalizer/FileEntityNormalizer.php b/core/modules/hal/src/Normalizer/FileEntityNormalizer.php
index ec870e9..d3b1797 100644
--- a/core/modules/hal/src/Normalizer/FileEntityNormalizer.php
+++ b/core/modules/hal/src/Normalizer/FileEntityNormalizer.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\hal\Normalizer;
 
+use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\hal\LinkManager\LinkManagerInterface;
@@ -9,6 +10,8 @@
 
 /**
  * Converts the Drupal entity object structure to a HAL array structure.
+ *
+ * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x.
  */
 class FileEntityNormalizer extends ContentEntityNormalizer {
 
@@ -27,6 +30,13 @@ class FileEntityNormalizer extends ContentEntityNormalizer {
   protected $httpClient;
 
   /**
+   * The hal settings config.
+   *
+   * @var \Drupal\Core\Config\Config
+   */
+  protected $halSettings;
+
+  /**
    * Constructs a FileEntityNormalizer object.
    *
    * @param \Drupal\Core\Entity\EntityManagerInterface $entity_manager
@@ -37,11 +47,14 @@ class FileEntityNormalizer extends ContentEntityNormalizer {
    *   The hypermedia link manager.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler.
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   The config factory.
    */
-  public function __construct(EntityManagerInterface $entity_manager, ClientInterface $http_client, LinkManagerInterface $link_manager, ModuleHandlerInterface $module_handler) {
+  public function __construct(EntityManagerInterface $entity_manager, ClientInterface $http_client, LinkManagerInterface $link_manager, ModuleHandlerInterface $module_handler, ConfigFactoryInterface $config_factory) {
     parent::__construct($link_manager, $entity_manager, $module_handler);
 
     $this->httpClient = $http_client;
+    $this->halSettings = $config_factory->get('hal.settings');
   }
 
   /**
@@ -49,8 +62,13 @@ public function __construct(EntityManagerInterface $entity_manager, ClientInterf
    */
   public function normalize($entity, $format = NULL, array $context = []) {
     $data = parent::normalize($entity, $format, $context);
-    // Replace the file url with a full url for the file.
-    $data['uri'][0]['value'] = $this->getEntityUri($entity);
+
+    $this->addCacheableDependency($context, $this->halSettings);
+
+    if ($this->halSettings->get('bc_file_uri_as_url_normalizer')) {
+      // Replace the file url with a full url for the file.
+      $data['uri'][0]['value'] = $this->getEntityUri($entity);
+    }
 
     return $data;
   }
diff --git a/core/modules/hal/tests/src/Functional/EntityResource/Media/MediaHalJsonAnonTest.php b/core/modules/hal/tests/src/Functional/EntityResource/Media/MediaHalJsonAnonTest.php
index c71b54e..66e1cc0 100644
--- a/core/modules/hal/tests/src/Functional/EntityResource/Media/MediaHalJsonAnonTest.php
+++ b/core/modules/hal/tests/src/Functional/EntityResource/Media/MediaHalJsonAnonTest.php
@@ -86,11 +86,6 @@ protected function getExpectedNormalizedEntity() {
               ],
             ],
             'lang' => 'en',
-            'uri' => [
-              [
-                'value' => $file->url(),
-              ],
-            ],
             'uuid' => [
               [
                 'value' => $file->uuid(),
@@ -126,11 +121,6 @@ protected function getExpectedNormalizedEntity() {
               ],
             ],
             'lang' => 'en',
-            'uri' => [
-              [
-                'value' => $thumbnail->url(),
-              ],
-            ],
             'uuid' => [
               [
                 'value' => $thumbnail->uuid(),
diff --git a/core/modules/hal/tests/src/Functional/FileDenormalizeTest.php b/core/modules/hal/tests/src/Functional/FileDenormalizeTest.php
index 05ee234..dbb708f 100644
--- a/core/modules/hal/tests/src/Functional/FileDenormalizeTest.php
+++ b/core/modules/hal/tests/src/Functional/FileDenormalizeTest.php
@@ -20,6 +20,17 @@ class FileDenormalizeTest extends BrowserTestBase {
    */
   public static $modules = ['hal', 'file', 'node'];
 
+  protected function setUp() {
+    parent::setUp();
+
+    // Override the default configuration to the hal BC setting is enabled, to
+    // return the full URL value as the file URI 'value'.
+    \Drupal::configFactory()
+      ->getEditable('hal.settings')
+      ->set('bc_file_uri_as_url_normalizer', TRUE)
+      ->save(TRUE);
+  }
+
   /**
    * Tests file entity denormalization.
    */
diff --git a/core/modules/hal/tests/src/Kernel/FileNormalizeTest.php b/core/modules/hal/tests/src/Kernel/FileNormalizeTest.php
index c4b67f5..355c09d 100644
--- a/core/modules/hal/tests/src/Kernel/FileNormalizeTest.php
+++ b/core/modules/hal/tests/src/Kernel/FileNormalizeTest.php
@@ -44,7 +44,10 @@ public function testNormalize() {
 
     $expected_array = [
       'uri' => [
-        ['value' => file_create_url($file->getFileUri())],
+        [
+          'value' => $file->getFileUri(),
+          'url' => file_url_transform_relative(file_create_url($file->getFileUri())),
+        ],
       ],
     ];
 
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php
index 1875d00..742d817 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\rest\Functional\EntityResource\Media;
 
+use Drupal\Core\Cache\Cache;
 use Drupal\file\Entity\File;
 use Drupal\media\Entity\Media;
 use Drupal\media\Entity\MediaType;
@@ -272,4 +273,11 @@ protected function getExpectedUnauthorizedAccessCacheability() {
       ->addCacheTags(['media:1']);
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedCacheTags() {
+    return Cache::mergeTags(parent::getExpectedCacheTags(), ['config:hal.settings']);
+  }
+
 }
diff --git a/core/tests/Drupal/Tests/Listeners/DeprecationListener.php b/core/tests/Drupal/Tests/Listeners/DeprecationListener.php
index 80b3d31..35fa2f0 100644
--- a/core/tests/Drupal/Tests/Listeners/DeprecationListener.php
+++ b/core/tests/Drupal/Tests/Listeners/DeprecationListener.php
@@ -113,6 +113,7 @@ public static function getSkippedDeprecations() {
       'Automatically creating the first item for computed fields is deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.0. Use \Drupal\Core\TypedData\ComputedItemListTrait instead.',
       '"\Drupal\Core\Entity\ContentEntityStorageBase::doLoadRevisionFieldItems()" is deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.0. "\Drupal\Core\Entity\ContentEntityStorageBase::doLoadMultipleRevisionsFieldItems()" should be implemented instead. See https://www.drupal.org/node/2924915.',
       'Passing a single revision ID to "\Drupal\Core\Entity\Sql\SqlContentEntityStorage::buildQuery()" is deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.0. An array of revision IDs should be given instead. See https://www.drupal.org/node/2924915.',
+      'The "serializer.normalizer.file_entity.hal" normalizer service is deprecated: it is obsolete, it only remains available for backwards compatibility.',
     ];
   }