They're the same architecture, but XMPP uses an extensible XML communication while Matrix uses an extensible JSON.
As far as I can tell, they're intended to do the same thing but are just implemented with different technologies.
I should also point out that there's a pretty well known Matrix-to-XMPP bridge called Bifrost (though I can't speak to it's quality or compatibility between surface-similar features)
@aaravchen Thanks, makes more sense now. Is there any inherent benefit to XML that would justify this development?
By using namespaces it's possible to extend and evolve the protocol over time, while maintaining backwards compatibility (as long as you want to). XMPP is 20 years old (!) and would be totally irrelevant now if it didn't have the ability to adapt to new technology and communication styles.
The core XMPP protocol was standardized at the IETF (the organization that develops and maintains many internet protocols such as HTTP and email) in 2004 and updated in 2011. But most of the protocol changes happen through documented extensions known as "XEPs".
New extensions are developed by the community and published at https://xmpp.org/extensions/
Due to XML namespaces, these extensions don't break existing software when they start getting used on the XMPP network.
To avoid chaos and confusion, each year updated guidance is published about which XEPs should be implemented by e.g. IM clients: https://xmpp.org/about/compliance-suites.html
The whole process is managed by the XMPP Standards Foundation (XSF), which is governed by community members: https://xmpp.org/about/xmpp-standards-foundation.html
This was so much more helpful than my 2 hours of trying to detangle the contentious arguments from biased enthusiasts' posts.
@vazub @mattj @aaravchen The Matrix experience is a lot more polished, since Matrix was designed for connection-less from the start, which works better for mobile, especially iOS. XMPP has extensions to work around XMPP being connection oriented, but that still has many problems in practice and the Matrix experience is a lot more polished. Configuring push notifications is done Server side in Matrix and works well and a huge pain point in XMPP, so MUCs + Mobile aren’t fun.
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