It is not a matrix client. I haven't dug too deep into their system, but it looks to me like a centralized server with additional steps (ie. still a single entity owning the server infrastructure)
From what I read in their documentation[1], session's network is built upon an onion routing system where nodes are registered in the OXEN blockchain; you stake 15000 $OXEN to create a node and if you are "well-behaved" you get rewards in that blockchain -- otherwise you lose your stake.
I haven't dug too deep either but it doesn't sound much more centralized than the tor network for example.
I haven't dug too deep either but it doesn't sound much more centralized than the tor network for example.
[1] https://docs.oxen.io/products-built-on-oxen/session/network-...