diff --git a/features/media-regenerate.feature b/features/media-regenerate.feature
index 6b48d1ad..edec0726 100644
--- a/features/media-regenerate.feature
+++ b/features/media-regenerate.feature
@@ -1933,3 +1933,103 @@ Feature: Regenerate WordPress attachments
       """
       site_icon-270
       """
+
+  Scenario: Update post content references when regenerating a specific image size
+    Given download:
+      | path                        | url                                      |
+      | {CACHE_DIR}/canola.jpg      | http://wp-cli.org/behat-data/canola.jpg  |
+    And a wp-content/mu-plugins/media-settings.php file:
+      """
+      <?php
+      add_action( 'after_setup_theme', function(){
+        add_image_size( 'test1', 400, 400, true );
+      });
+      """
+    And I run `wp option update uploads_use_yearmonth_folders 0`
+
+    When I run `wp media import {CACHE_DIR}/canola.jpg --title="My imported attachment" --porcelain`
+    Then save STDOUT as {ATTACHMENT_ID}
+    And the wp-content/uploads/canola-400x400.jpg file should exist
+
+    # Get the full URL of the test1 thumbnail.
+    When I run `wp eval "echo wp_get_attachment_image_src( {ATTACHMENT_ID}, 'test1' )[0];"`
+    Then save STDOUT as {OLD_THUMBNAIL_URL}
+
+    # Create a post referencing the old thumbnail URL in post content.
+    When I run `wp post create --post_title="Test Post" --post_status=publish --post_content="{OLD_THUMBNAIL_URL}" --porcelain`
+    Then save STDOUT as {POST_ID}
+
+    # Confirm the old URL is in post content before regeneration.
+    When I run `wp post get {POST_ID} --field=post_content`
+    Then STDOUT should contain:
+      """
+      canola-400x400.jpg
+      """
+
+    # Change "test1" image size dimensions.
+    Given a wp-content/mu-plugins/media-settings.php file:
+      """
+      <?php
+      add_action( 'after_setup_theme', function(){
+        add_image_size( 'test1', 350, 350, true );
+      });
+      """
+
+    # Regenerate "test1" without --update-attachment-refs - post content should be unchanged.
+    When I run `wp media regenerate {ATTACHMENT_ID} --image_size=test1 --yes`
+    Then STDOUT should contain:
+      """
+      1/1 Regenerated "test1" thumbnail for "My imported attachment"
+      """
+    And the wp-content/uploads/canola-350x350.jpg file should exist
+
+    When I run `wp post get {POST_ID} --field=post_content`
+    Then STDOUT should contain:
+      """
+      canola-400x400.jpg
+      """
+
+    # Change "test1" back to 400x400 so we can test --update-attachment-refs.
+    Given a wp-content/mu-plugins/media-settings.php file:
+      """
+      <?php
+      add_action( 'after_setup_theme', function(){
+        add_image_size( 'test1', 400, 400, true );
+      });
+      """
+    When I run `wp media regenerate {ATTACHMENT_ID} --image_size=test1 --yes`
+    Then STDOUT should contain:
+      """
+      1/1 Regenerated "test1" thumbnail for "My imported attachment"
+      """
+    And the wp-content/uploads/canola-400x400.jpg file should exist
+
+    # Change "test1" to 350x350 and regenerate with --update-attachment-refs.
+    Given a wp-content/mu-plugins/media-settings.php file:
+      """
+      <?php
+      add_action( 'after_setup_theme', function(){
+        add_image_size( 'test1', 350, 350, true );
+      });
+      """
+    When I run `wp media regenerate {ATTACHMENT_ID} --image_size=test1 --update-attachment-refs --yes`
+    Then STDOUT should contain:
+      """
+      1/1 Regenerated "test1" thumbnail for "My imported attachment"
+      """
+    And STDOUT should contain:
+      """
+      Success: Regenerated 1 of 1 images.
+      """
+    And the wp-content/uploads/canola-350x350.jpg file should exist
+
+    # Confirm the post content was updated to use the new thumbnail URL.
+    When I run `wp post get {POST_ID} --field=post_content`
+    Then STDOUT should contain:
+      """
+      canola-350x350.jpg
+      """
+    And STDOUT should not contain:
+      """
+      canola-400x400.jpg
+      """
diff --git a/src/Media_Command.php b/src/Media_Command.php
index 1fc15663..3dd7636a 100644
--- a/src/Media_Command.php
+++ b/src/Media_Command.php
@@ -1,6 +1,7 @@
 <?php
 
 use WP_CLI\Utils;
+use WP_CLI\Path;
 
 /**
  * Imports files as attachments, regenerates thumbnails, or lists registered image sizes.
@@ -74,6 +75,9 @@ class Media_Command extends WP_CLI_Command {
 	 * [--delete-unknown]
 	 * : Only delete thumbnails for old unregistered image sizes.
 	 *
+	 * [--update-attachment-refs]
+	 * : Update references to regenerated thumbnails in post content.
+	 *
 	 * [--yes]
 	 * : Answer yes to the confirmation message. Confirmation only shows when no IDs passed as arguments.
 	 *
@@ -123,7 +127,7 @@ class Media_Command extends WP_CLI_Command {
 	 *     Success: Regenerated 3 of 3 images.
 	 *
 	 * @param string[] $args Positional arguments.
-	 * @param array{image_size?: string|string[], 'skip-delete'?: bool, 'only-missing'?: bool, 'delete-unknown'?: bool, yes?: bool} $assoc_args Associative arguments.
+	 * @param array{image_size?: string|string[], 'skip-delete'?: bool, 'only-missing'?: bool, 'delete-unknown'?: bool, 'update-attachment-refs'?: bool, yes?: bool} $assoc_args Associative arguments.
 	 * @return void
 	 */
 	public function regenerate( $args, $assoc_args = array() ) {
@@ -172,6 +176,8 @@ public function regenerate( $args, $assoc_args = array() ) {
 			$skip_delete = false;
 		}
 
+		$update_attachment_refs = Utils\get_flag_value( $assoc_args, 'update-attachment-refs' );
+
 		$additional_mime_types = array();
 
 		if ( Utils\wp_version_compare( '4.7', '>=' ) ) {
@@ -212,7 +218,7 @@ public function regenerate( $args, $assoc_args = array() ) {
 				// @phpstan-ignore function.deprecated
 				Utils\wp_clear_object_cache();
 			}
-			$this->process_regeneration( $post_id, $skip_delete, $only_missing, $delete_unknown, $image_sizes, $number . '/' . $count, $successes, $errors, $skips );
+			$this->process_regeneration( $post_id, $skip_delete, $only_missing, $delete_unknown, $image_sizes, $update_attachment_refs, $number . '/' . $count, $successes, $errors, $skips );
 		}
 
 		if ( isset( $image_size_filters ) ) {
@@ -384,7 +390,7 @@ public function import( $args, $assoc_args = array() ) {
 				} else {
 					$tempfile = $this->make_copy( $file );
 				}
-				$name = Utils\basename( $file );
+				$name = Path::basename( $file );
 
 				if ( Utils\get_flag_value( $assoc_args, 'preserve-filetime' ) ) {
 					$file_time = @filemtime( $file );
@@ -402,7 +408,7 @@ public function import( $args, $assoc_args = array() ) {
 					++$errors;
 					continue;
 				}
-				$name = (string) strtok( Utils\basename( $file ), '?' );
+				$name = (string) strtok( Path::basename( $file ), '?' );
 			}
 
 			if ( ! empty( $assoc_args['file_name'] ) ) {
@@ -448,7 +454,7 @@ public function import( $args, $assoc_args = array() ) {
 			}
 
 			if ( empty( $post_array['post_title'] ) ) {
-				$post_array['post_title'] = preg_replace( '/\.[^.]+$/', '', Utils\basename( $file ) );
+				$post_array['post_title'] = preg_replace( '/\.[^.]+$/', '', Path::basename( $file ) );
 			}
 
 			if ( Utils\get_flag_value( $assoc_args, 'skip-copy' ) ) {
@@ -679,7 +685,7 @@ private function gcd( $num1, $num2 ) {
 	 */
 	private function make_copy( $path ) {
 		$dir      = get_temp_dir();
-		$filename = Utils\basename( $path );
+		$filename = Path::basename( $path );
 		if ( empty( $filename ) ) {
 			$filename = (string) time();
 		}
@@ -715,6 +721,7 @@ private function get_image_sizes_description( array $sizes, $noun, $default_if_e
 	 * @param bool $only_missing
 	 * @param bool $delete_unknown
 	 * @param string[] $image_sizes
+	 * @param bool $update_attachment_refs
 	 * @param string $progress
 	 * @param int $successes
 	 * @param int $errors
@@ -724,7 +731,7 @@ private function get_image_sizes_description( array $sizes, $noun, $default_if_e
 	 * @param-out int $skips
 	 * @return void
 	 */
-	private function process_regeneration( $id, $skip_delete, $only_missing, $delete_unknown, $image_sizes, $progress, &$successes, &$errors, &$skips ) {
+	private function process_regeneration( $id, $skip_delete, $only_missing, $delete_unknown, $image_sizes, $update_attachment_refs, $progress, &$successes, &$errors, &$skips ) {
 
 		$title = get_the_title( $id );
 		if ( '' === $title ) {
@@ -752,6 +759,20 @@ private function process_regeneration( $id, $skip_delete, $only_missing, $delete
 
 		$original_meta = wp_get_attachment_metadata( $id );
 
+		$old_size_urls = array();
+		if ( $update_attachment_refs && is_array( $original_meta ) && ! empty( $original_meta['sizes'] ) ) {
+			$attachment_url = wp_get_attachment_url( $id );
+			if ( $attachment_url ) {
+				$dir_url        = trailingslashit( dirname( $attachment_url ) );
+				$sizes_to_track = $image_sizes ?: array_keys( $original_meta['sizes'] );
+				foreach ( $sizes_to_track as $size ) {
+					if ( ! empty( $original_meta['sizes'][ $size ]['file'] ) ) {
+						$old_size_urls[ $size ] = $dir_url . $original_meta['sizes'][ $size ]['file'];
+					}
+				}
+			}
+		}
+
 		if ( $delete_unknown ) {
 			$this->delete_unknown_image_sizes( $id, $fullsizepath );
 
@@ -846,6 +867,35 @@ private function process_regeneration( $id, $skip_delete, $only_missing, $delete
 
 			WP_CLI::log( "$progress Regenerated thumbnails for $att_desc." );
 		}
+
+		if ( $update_attachment_refs && ! empty( $old_size_urls ) && is_array( $metadata ) && ! empty( $metadata['sizes'] ) ) {
+			$attachment_url = wp_get_attachment_url( $id );
+			if ( $attachment_url ) {
+				$dir_url = trailingslashit( dirname( $attachment_url ) );
+				/**
+				 * @var array<string, array<string, mixed>> $new_sizes
+				 */
+				$new_sizes        = is_array( $metadata['sizes'] ) ? $metadata['sizes'] : array();
+				$url_replacements = array();
+				foreach ( $old_size_urls as $size => $old_url ) {
+					$size_data = $new_sizes[ $size ] ?? null;
+					if ( ! is_array( $size_data ) || empty( $size_data['file'] ) ) {
+						continue;
+					}
+					/**
+					 * @var array{file: string} $size_data
+					 */
+					$new_url = $dir_url . $size_data['file'];
+					if ( $old_url !== $new_url ) {
+						$url_replacements[ $old_url ] = $new_url;
+					}
+				}
+				if ( ! empty( $url_replacements ) ) {
+					$this->update_post_content_for_attachment( $url_replacements );
+				}
+			}
+		}
+
 		++$successes;
 	}
 
@@ -1762,4 +1812,62 @@ private function delete_unknown_image_sizes( $id, $fullsizepath ) {
 		// @phpstan-ignore argument.type
 		wp_update_attachment_metadata( $id, $original_meta );
 	}
+
+	/**
+	 * Updates post content replacing old attachment URLs with new ones in a single query.
+	 *
+	 * Applies all replacements as nested REPLACE() calls so only one table scan is needed.
+	 *
+	 * @param array<string, string> $url_replacements Map of old URL => new URL.
+	 * @return void
+	 */
+	private function update_post_content_for_attachment( array $url_replacements ) {
+		global $wpdb;
+
+		if ( empty( $url_replacements ) ) {
+			return;
+		}
+
+		$replace_expr  = 'post_content';
+		$replace_args  = array();
+		$where_clauses = array();
+		$where_args    = array();
+
+		foreach ( $url_replacements as $old_url => $new_url ) {
+			$replace_expr    = "REPLACE($replace_expr, %s, %s)";
+			$replace_args[]  = $old_url;
+			$replace_args[]  = $new_url;
+			$where_clauses[] = 'post_content LIKE %s';
+			$where_args[]    = '%' . $wpdb->esc_like( $old_url ) . '%';
+		}
+
+		$where_sql = implode( ' OR ', $where_clauses );
+
+		// First, find the IDs of posts whose content will be updated so we can clear their object cache entries.
+		// phpcs:disable WordPress.DB.PreparedSQL.NotPrepared,WordPress.DB.PreparedSQL.InterpolatedNotPrepared,WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
+		$post_ids = $wpdb->get_col(
+			$wpdb->prepare(
+				"SELECT ID FROM {$wpdb->posts} WHERE post_type <> 'revision' AND ({$where_sql})",
+				...$where_args
+			)
+		);
+
+		$result = $wpdb->query(
+			$wpdb->prepare(
+				"UPDATE {$wpdb->posts} SET post_content = {$replace_expr} WHERE post_type <> 'revision' AND ({$where_sql})",
+				...array_merge( $replace_args, $where_args )
+			)
+		);
+		// phpcs:enable WordPress.DB.PreparedSQL.NotPrepared,WordPress.DB.PreparedSQL.InterpolatedNotPrepared,WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
+		if ( false === $result ) {
+			WP_CLI::warning( 'Failed to update post content references for attachment.' );
+		} else {
+			if ( ! empty( $post_ids ) ) {
+				foreach ( $post_ids as $post_id ) {
+					clean_post_cache( (int) $post_id );
+				}
+			}
+			wp_cache_set( 'last_changed', microtime(), 'posts' );
+		}
+	}
 }