Source

File: wp-includes/post.php

function is_sticky( $post_id = 0 ) {
	$post_id = absint( $post_id );

	if ( ! $post_id ) {
		$post_id = get_the_ID();
	}

	$stickies = get_option( 'sticky_posts' );

	if ( is_array( $stickies ) ) {
		$stickies  = array_map( 'intval', $stickies );
		$is_sticky = in_array( $post_id, $stickies, true );
	} else {
		$is_sticky = false;
	}

	/**
	 * Filters whether a post is sticky.
	 *
	 * @since 5.3.0
	 *
	 * @param bool $is_sticky Whether a post is sticky.
	 * @param int  $post_id   Post ID.
	 */
	return apply_filters( 'is_sticky', $is_sticky, $post_id );
}