I even made a dedicated SourceMod plugin for this (link valid for 30 days):
https://transfert.free.fr/mt4wpja
It prompts players to add +cl_interp 0 to their CS:S launch options. This bypasses the Steam Cloud, which constantly overwrites the value back to 0.031ms (since cl_interp is a client-side command that a server cannot physically force on a player).
The other "modern" netcode commands can be enforced directly through the server.cfg:
sv_minrate 100000
sv_maxrate 0
sv_mincmdrate 66
sv_maxcmdrate 66
sv_minupdaterate 66
sv_maxupdaterate 66
sv_client_min_interp_ratio "1"
sv_client_max_interp_ratio "2"
sv_client_cmdrate_difference "0"
sv_competitive_minspec 1
The plugin monitors the player's ping:
If ping < 60ms: Sets the player to ratio 1 (Competitive, 1-tick buffer).
If ping > 60ms: Sets the player to ratio 2 (Safe, 2-tick buffer).
With this setup, you won't have players sending only 30 cmd/s and receiving only 20/s while the server is calculating at 66.66. More importantly, it fixes the 100ms interpolation issue, where a player's game only refreshes what’s actually happening on the server every 100ms, instead of every 15.2ms (ratio 1) or 30.3ms (ratio 2).