No, and the reasoning is worth following, because "open source the server" sounds like it would help more than it does. All client apps are fully open source, and iOS and Android support verifiable builds. Publishing the server code would add no comparable guarantee.
What verifiable builds actually prove
Publishing source proves nothing on its own if the binary in the app store was built from something else. A verifiable build lets anyone rebuild the app from the published code and confirm that the result matches what Google Play or the App Store delivered. That closes the gap between the code you can read and the software you are running, and it is the step most open-source claims never take.
Why the same argument does not extend to a server
There is no way to verify that a server is running the code somebody published. You can read it, compile it, and compare it to nothing, because the machine executing it is not yours and cannot be inspected from outside. Published server code tells you what a company says it runs. It cannot tell you what it runs. That is not a shortcoming in disclosure, it is a property of running software on hardware you do not control.
What this means for each kind of chat
- Secret Chats. The guarantee comes from the client, which is open and verifiable. The server relays ciphertext it cannot read, so its code is not what protects you.
- Cloud chats. Protection comes from the architecture: keys split into parts and held separately from the data, across different jurisdictions. That is a structural property rather than something a code listing would demonstrate.
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