diff --git a/ops/machines/nevsky/default.nix b/ops/machines/nevsky/default.nix
index 8453415da..3b8d8a156 100644
--- a/ops/machines/nevsky/default.nix
+++ b/ops/machines/nevsky/default.nix
@@ -208,6 +208,10 @@ in
 
   services.depot.builderball.enable = true;
 
+  # Use TVL cache locally through the proxy; for cross-builder substitution.
+  tvl.cache.enable = true;
+  tvl.cache.builderball = true;
+
   security.sudo.extraRules = [{
     groups = [ "wheel" ];
     commands = [{ command = "ALL"; options = [ "NOPASSWD" ]; }];
diff --git a/ops/machines/whitby/default.nix b/ops/machines/whitby/default.nix
index 8c0b7d184..786b24000 100644
--- a/ops/machines/whitby/default.nix
+++ b/ops/machines/whitby/default.nix
@@ -674,5 +674,9 @@ in
 
   zramSwap.enable = true;
 
+  # Use TVL cache locally through the proxy; for cross-builder substitution.
+  tvl.cache.enable = true;
+  tvl.cache.builderball = true;
+
   system.stateVersion = "20.03";
 }
diff --git a/ops/modules/tvl-cache.nix b/ops/modules/tvl-cache.nix
index 683818d10..e6edacf80 100644
--- a/ops/modules/tvl-cache.nix
+++ b/ops/modules/tvl-cache.nix
@@ -3,6 +3,7 @@
 {
   options = {
     tvl.cache.enable = lib.mkEnableOption "the TVL binary cache";
+    tvl.cache.builderball = lib.mkEnableOption "use experimental builderball cache";
   };
 
   config = lib.mkIf config.tvl.cache.enable {
@@ -12,7 +13,9 @@
       ];
 
       substituters = [
-        "https://cache.tvl.su"
+        (if config.tvl.cache.builderball
+        then "https://cache.tvl.fyi"
+        else "https://cache.tvl.su")
       ];
     };
   };
diff --git a/users/tazjin/nixos/tverskoy/default.nix b/users/tazjin/nixos/tverskoy/default.nix
index 95b6a9ef1..353a03bad 100644
--- a/users/tazjin/nixos/tverskoy/default.nix
+++ b/users/tazjin/nixos/tverskoy/default.nix
@@ -28,6 +28,7 @@ lib.fix (self: {
   ] ++ lib.optional (builtins.pathExists ./local-config.nix) ./local-config.nix;
 
   tvl.cache.enable = true;
+  tvl.cache.builderball = true;
 
   boot = {
     initrd.availableKernelModules = [ "nvme" "ehci_pci" "xhci_pci" "usb_storage" "sd_mod" "rtsx_pci_sdmmc" ];