Get the number of internal links linking to a post and the number of outgoing internal links from Yoast indexable using their models.

get-internal-links-from-yoast.php

<?php

  if ( !class_exists( '\Yoast\WP\Lib\Model' ) || !class_exists( '\Yoast\WP\SEO\Models\Indexable' ) ) {
    return;
  }

  // The post ID
  $object_id = 123; 

  // The post object type (post type)
  $object_type = 'post'; 

  /* @var $indexable \Yoast\WP\SEO\Models\Indexable */
  $indexable = \Yoast\WP\Lib\Model::of_type( 'Indexable' )->where( 'object_id', $object_id )
    ->where( 'object_type', $object_type )
    ->find_one();

  // Number of internal links linking to the post ID
  $internal_links = (int) $indexable->incoming_link_count;

  // Number of outgoing internal links to the post ID
  $outgoing_links = (int) $indexable->link_count;


?>