How to access a list's length in a template's code block for Django?

In a template, I have a variable of type list called "participants". I want to check if the length of the list is equal to 2, for example. I tried the following:

{{ participants | json_script:"participants"}}

{% if participants|length==2 %}

.....
{% endif %}

However, this does not work. The error I get is:

TemplateSyntaxError at /chat/lobby/
Could not parse the remainder: ‘==2’ from ‘participants.count==2’

Can someone point out a way to access a list’s length in a template’s code block? thank you for your time and consideration!

{% if participants|length == 2 %}
…
{% endif %}