diff --git a/src/plugin/config/loader.test.ts b/src/plugin/config/loader.test.ts
new file mode 100644
index 0000000..6da8c13
--- /dev/null
+++ b/src/plugin/config/loader.test.ts
@@ -0,0 +1,83 @@
+import { existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { __testExports, loadConfig } from "./loader";
+
+describe("config loader legacy Windows migration", () => {
+  let tempRoot: string;
+  let previousConfigDir: string | undefined;
+  let previousAppData: string | undefined;
+
+  beforeEach(() => {
+    tempRoot = mkdtempSync(join(tmpdir(), "antigravity-config-"));
+
+    previousConfigDir = process.env.OPENCODE_CONFIG_DIR;
+    previousAppData = process.env.APPDATA;
+
+    process.env.OPENCODE_CONFIG_DIR = join(tempRoot, "new-config");
+    process.env.APPDATA = join(tempRoot, "legacy-appdata");
+  });
+
+  afterEach(() => {
+    if (previousConfigDir === undefined) {
+      delete process.env.OPENCODE_CONFIG_DIR;
+    } else {
+      process.env.OPENCODE_CONFIG_DIR = previousConfigDir;
+    }
+
+    if (previousAppData === undefined) {
+      delete process.env.APPDATA;
+    } else {
+      process.env.APPDATA = previousAppData;
+    }
+
+    rmSync(tempRoot, { recursive: true, force: true });
+  });
+
+  it("migrates %APPDATA%/opencode/antigravity.json to current config path", () => {
+    const legacyDir = join(process.env.APPDATA!, "opencode");
+    const legacyPath = join(legacyDir, "antigravity.json");
+    const expectedPath = join(process.env.OPENCODE_CONFIG_DIR!, "antigravity.json");
+
+    mkdirSync(legacyDir, { recursive: true });
+    writeFileSync(legacyPath, JSON.stringify({ scheduling_mode: "performance_first" }), "utf-8");
+
+    const resolvedPath = __testExports.resolveUserConfigPath("win32");
+
+    expect(resolvedPath).toBe(expectedPath);
+    expect(existsSync(expectedPath)).toBe(true);
+    expect(existsSync(legacyPath)).toBe(false);
+  });
+
+  it("loads settings from migrated legacy config", () => {
+    const legacyDir = join(process.env.APPDATA!, "opencode");
+    const legacyPath = join(legacyDir, "antigravity.json");
+
+    mkdirSync(legacyDir, { recursive: true });
+    writeFileSync(
+      legacyPath,
+      JSON.stringify({
+        account_selection_strategy: "round-robin",
+        scheduling_mode: "performance_first",
+        switch_on_first_rate_limit: true,
+        max_rate_limit_wait_seconds: 5,
+      }),
+      "utf-8",
+    );
+
+    // Force legacy -> new path migration even when tests run on non-Windows CI.
+    __testExports.resolveUserConfigPath("win32");
+
+    const loaded = loadConfig(tempRoot);
+
+    expect(loaded.account_selection_strategy).toBe("round-robin");
+    expect(loaded.scheduling_mode).toBe("performance_first");
+    expect(loaded.switch_on_first_rate_limit).toBe(true);
+    expect(loaded.max_rate_limit_wait_seconds).toBe(5);
+
+    const migratedPath = join(process.env.OPENCODE_CONFIG_DIR!, "antigravity.json");
+    const persisted = JSON.parse(readFileSync(migratedPath, "utf-8")) as Record<string, unknown>;
+    expect(persisted.scheduling_mode).toBe("performance_first");
+  });
+});
diff --git a/src/plugin/config/loader.ts b/src/plugin/config/loader.ts
index 328a663..d7b952a 100644
--- a/src/plugin/config/loader.ts
+++ b/src/plugin/config/loader.ts
@@ -9,8 +9,8 @@
  * 4. Environment variables
  */
 
-import { existsSync, readFileSync } from "node:fs";
-import { join } from "node:path";
+import { copyFileSync, existsSync, mkdirSync, readFileSync, renameSync, unlinkSync } from "node:fs";
+import { dirname, join } from "node:path";
 import { homedir } from "node:os";
 import { AccountSelectionStrategySchema, AntigravityConfigSchema, DEFAULT_CONFIG, type AntigravityConfig } from "./schema";
 import { createLogger } from "../logger";
@@ -37,11 +37,61 @@ function getConfigDir(): string {
   return join(xdgConfig, "opencode");
 }
 
+/**
+ * Gets the legacy Windows config directory (%APPDATA%\opencode).
+ */
+function getLegacyWindowsConfigDir(): string {
+  return join(
+    process.env.APPDATA || join(homedir(), "AppData", "Roaming"),
+    "opencode",
+  );
+}
+
+/**
+ * Resolves user config path and migrates legacy Windows config if needed.
+ *
+ * Legacy path: %APPDATA%\opencode\antigravity.json
+ * Current path: ~/.config/opencode/antigravity.json (or OPENCODE_CONFIG_DIR override)
+ */
+function resolveUserConfigPath(platform: NodeJS.Platform = process.platform): string {
+  const newPath = join(getConfigDir(), "antigravity.json");
+
+  if (platform !== "win32") {
+    return newPath;
+  }
+
+  const legacyPath = join(getLegacyWindowsConfigDir(), "antigravity.json");
+  if (!existsSync(legacyPath) || existsSync(newPath)) {
+    return newPath;
+  }
+
+  try {
+    mkdirSync(dirname(newPath), { recursive: true });
+    try {
+      renameSync(legacyPath, newPath);
+      log.info("Migrated Windows config via rename", { from: legacyPath, to: newPath });
+    } catch {
+      copyFileSync(legacyPath, newPath);
+      unlinkSync(legacyPath);
+      log.info("Migrated Windows config via copy+delete", { from: legacyPath, to: newPath });
+    }
+    return newPath;
+  } catch (error) {
+    // Fallback to legacy path if migration failed, so user settings are still respected.
+    log.warn("Failed to migrate legacy Windows config, falling back to legacy path", {
+      legacyPath,
+      newPath,
+      error: String(error),
+    });
+    return legacyPath;
+  }
+}
+
 /**
  * Get the user-level config file path.
  */
 export function getUserConfigPath(): string {
-  return join(getConfigDir(), "antigravity.json");
+  return resolveUserConfigPath();
 }
 
 /**
@@ -231,3 +281,7 @@ export function initRuntimeConfig(config: AntigravityConfig): void {
 export function getKeepThinking(): boolean {
   return runtimeConfig?.keep_thinking ?? false;
 }
+
+export const __testExports = {
+  resolveUserConfigPath,
+};