diff --git a/apps/server/src/terminal/Manager.test.ts b/apps/server/src/terminal/Manager.test.ts
index d89316cc74951..6fbcd4ffba84b 100644
--- a/apps/server/src/terminal/Manager.test.ts
+++ b/apps/server/src/terminal/Manager.test.ts
@@ -1944,6 +1944,20 @@ it.layer(
     }),
   );
 
+  it.effect("expands a provider home named in any case on Windows", () =>
+    Effect.gen(function* () {
+      const path = yield* Path.Path;
+      const home = yield* HostProcess.HomeDirectory;
+      const { manager, ptyAdapter } = yield* createManager(5, {
+        env: { GROK_HOME: "C:\\inherited-grok" },
+      });
+
+      yield* manager.open(openInput({ env: { grok_home: "~/.grok-work" } }));
+
+      expect(ptyAdapter.spawnInputs[0]?.env.GROK_HOME).toBe(path.join(home, ".grok-work"));
+    }).pipe(Effect.provide(layerWithHostPlatform("win32"))),
+  );
+
   it.effect("fails closed when a provider instance is missing", () =>
     Effect.gen(function* () {
       const providerInstanceId = ProviderInstanceId.make("deleted_instance");
diff --git a/apps/server/src/terminal/Manager.ts b/apps/server/src/terminal/Manager.ts
index 3ee43635f45c5..839d7ad27e7b0 100644
--- a/apps/server/src/terminal/Manager.ts
+++ b/apps/server/src/terminal/Manager.ts
@@ -69,7 +69,7 @@ import { makeClaudeEnvironment } from "../provider/Drivers/ClaudeHome.ts";
 import { deriveProviderInstanceConfigMap } from "../provider/ProviderInstanceRegistryHydration.ts";
 import * as ServerSettings from "../serverSettings.ts";
 import { increment, terminalSessionsTotal } from "../observability/Metrics.ts";
-import { expandHomePath } from "@t3tools/provider-core/server/pathExpansion";
+import { expandHomeVariable } from "@t3tools/provider-core/server/pathExpansion";
 import * as ProcessRunner from "../processRunner.ts";
 import * as PortScanner from "../preview/PortScanner.ts";
 import * as NativeTelemetryClient from "../resourceTelemetry/NativeTelemetryClient.ts";
@@ -1367,8 +1367,11 @@ function createTerminalSpawnEnv(
         platform === "win32"
           ? Object.keys(spawnEnv).find((candidate) => candidate.toLowerCase() === key.toLowerCase())
           : undefined;
-      spawnEnv[existingKey ?? key] =
-        key === "CODEX_HOME" || key === "CLAUDE_CONFIG_DIR" ? expandHomePath(value, home) : value;
+      spawnEnv[existingKey ?? key] = expandHomeVariable(
+        platform === "win32" ? key.toUpperCase() : key,
+        value,
+        home,
+      );
     }
   }
   if (!spawnEnv.COLORTERM && runtimeEnv?.COLORTERM === undefined) {
diff --git a/packages/provider-core/src/server/instanceEnvironment.test.ts b/packages/provider-core/src/server/instanceEnvironment.test.ts
index 114905d3f2115..374559f7f099a 100644
--- a/packages/provider-core/src/server/instanceEnvironment.test.ts
+++ b/packages/provider-core/src/server/instanceEnvironment.test.ts
@@ -17,11 +17,13 @@ describe("mergeProviderInstanceEnvironment", () => {
       const baseEnv = {
         CODEX_HOME: "~/.inherited-codex",
         CLAUDE_CONFIG_DIR: "~/.inherited-claude",
+        GROK_HOME: "~/.inherited-grok",
       };
       const environment = yield* mergeProviderInstanceEnvironment(
         [
           { name: "CODEX_HOME", value, sensitive: false },
           { name: "CLAUDE_CONFIG_DIR", value, sensitive: false },
+          { name: "GROK_HOME", value, sensitive: false },
           { name: "CUSTOM_VALUE", value, sensitive: false },
         ],
         baseEnv,
@@ -30,11 +32,13 @@ describe("mergeProviderInstanceEnvironment", () => {
       expect(environment).toEqual({
         CODEX_HOME: path.join("/home/ada", tail),
         CLAUDE_CONFIG_DIR: path.join("/home/ada", tail),
+        GROK_HOME: path.join("/home/ada", tail),
         CUSTOM_VALUE: value,
       });
       expect(baseEnv).toEqual({
         CODEX_HOME: "~/.inherited-codex",
         CLAUDE_CONFIG_DIR: "~/.inherited-claude",
+        GROK_HOME: "~/.inherited-grok",
       });
     }).pipe(
       Effect.provideService(HostProcess.HomeDirectory, "/home/ada"),
diff --git a/packages/provider-core/src/server/instanceEnvironment.ts b/packages/provider-core/src/server/instanceEnvironment.ts
index 470f7e70dc616..0ade572984275 100644
--- a/packages/provider-core/src/server/instanceEnvironment.ts
+++ b/packages/provider-core/src/server/instanceEnvironment.ts
@@ -2,7 +2,7 @@ import type { ProviderInstanceEnvironment } from "@t3tools/contracts";
 import * as HostProcess from "@t3tools/shared/HostProcess";
 import * as Effect from "effect/Effect";
 
-import { expandHomePath } from "./pathExpansion.ts";
+import { expandHomeVariable } from "./pathExpansion.ts";
 
 export const mergeProviderInstanceEnvironment = Effect.fn(function* (
   environment: ProviderInstanceEnvironment | undefined,
@@ -27,10 +27,7 @@ export const mergeProviderInstanceEnvironment = Effect.fn(function* (
         if (inherited.toUpperCase() === name) delete next[inherited];
       }
     }
-    next[name] =
-      name === "CODEX_HOME" || name === "CLAUDE_CONFIG_DIR"
-        ? expandHomePath(variable.value, home)
-        : variable.value;
+    next[name] = expandHomeVariable(name, variable.value, home);
   }
   return next;
 });
diff --git a/packages/provider-core/src/server/pathExpansion.ts b/packages/provider-core/src/server/pathExpansion.ts
index 9a3822b836312..6c5eab795000e 100644
--- a/packages/provider-core/src/server/pathExpansion.ts
+++ b/packages/provider-core/src/server/pathExpansion.ts
@@ -10,3 +10,9 @@ export function expandHomePath(value: string, home: string): string {
   }
   return value;
 }
+
+const HOME_PATH_VARIABLES = new Set(["CODEX_HOME", "CLAUDE_CONFIG_DIR", "GROK_HOME"]);
+
+export function expandHomeVariable(name: string, value: string, home: string): string {
+  return HOME_PATH_VARIABLES.has(name) ? expandHomePath(value, home) : value;
+}