It's probably easy to do with Java / C# and Go, they're using a 36 cores machine to achieve that with fast CPU, meaning that you need 3000conn/sec per core, very doable with recent frameworks.
We run about 20k connections per second with nodejs on a 12 core machine.
All node is doing is parsing cached JSON, modifies it and serve it back to the client.
One server has an uptime of 560days without any memory/performance issues.
The order of magnitude(s) differentiator for server performance really comes down to whether or not the architecture is blocking or non-blocking.