The game console doesn't detect hidehud 1 and drawhud 0 (or cl_hidehud/cl_drawhud) commands, these may have worked in the past before the game was transferred to OpenGL.
"Cheats" are probably required, can be enabled with sv_cheats 1 command.
Half-Life – How to Disable HUD in Half-Life
half-life
Best Answer
The
hud_draw 0should do the trick just fine for you.Should you require to also remove the crosshair, then
crosshair 0will help.