GoToWebinar Web Platform / Instant Join App - how to use the 'new/updated' web platform?

Hello,

We're very interested in only using the web application also known as 'Instant join app', instead of downloading software, as some of our customers are simply unable to download software, due to firewall rules etc. 

From my understanding there is currently two ways to enable the web platform:

Using 'Webcast' as the webinar type.

Adding a '?clientType=html5' parameter to the joinURL for each participant. 

The interface then looks like this:

HOWEVER, today we noticed somebody else hosting a webinar with GoToWebinar, with the web app looking different:

Notice how the 'new' platform is white, aligned to the left and is more 'clean/modern'.

Now to my question: WHAT is the difference between these two, if any at all - and how can we use the new version automatically? 

The only way i managed to get the new interface for our own webinars, was by pasting a participant joinURL through this page:  https://app.gotowebinar.com/unified/index.html#/

Which then redirected me to:

https://app.gotowebinar.com/unified/index.html#/webinar/7067194960674782220/attend/3854012965987818510

The 'old' way, of simply just clicking the joinURL redirects to:

https://app.gotowebinar.com/index.html#788768355/7067194960674782220/3854012965987818510

So the difference is that the 'new' url contains '/unified/', '/webinar/' & '/attend/'

But any information regarding webcast/instant join app is very limited. If the 'new' platform is better than the old one, how can we automatically/programmatically make sure that the participant gets that version, without them having to go through the 'unified' page, to paste their joinURL? I can't find any API resource regarding 'unified'