How can i display tokens with html tags? On assigning tokens(both custom and exisiting tokens) with values like  

$replacements[$original] = "&lt;b&gt;Hello&lt;/b&gt;";


and then using that token either in full html or any other text format(all the text formats) it displays on the screen &lt;b&gt;Hello&lt;/b&gt; i.e actual tags are being rendered instead of Hello . Same is happening with other html tags i.e entire &lt;div&gt; &lt;p&gt; all the html tags get display. 
This although does not happen in Drupal 7.

Is there any configuration i am missing? How to render html values properly using tokens?
Try this one - 

$replacements[$original] = \Drupal\Core\Render\Markup::create("&lt;b&gt;Hello&lt;/b&gt;");


Helpful links:

https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21Markup.php/class/Markup/8.2.x

http://www.drupaldump.com/drupal-8-how-have-custom-tokens-html-them-properly-replaced