diff --git a/spec/__support__/filesync.ts b/spec/__support__/filesync.ts
index 358b9ac68..1ba12badc 100644
--- a/spec/__support__/filesync.ts
+++ b/spec/__support__/filesync.ts
@@ -206,7 +206,12 @@ export const makeSyncScenario = async ({
     await localDir.loadIgnoreFile();
 
     if (!localFiles[".gadget/sync.json"]) {
-      const syncJson: SyncJson = { app: testApp.slug, environment: "development", filesVersion: "1", mtime: Date.now() + 1 };
+      const syncJson: SyncJson = {
+        app: testApp.slug,
+        filesVersion: "1",
+        currentEnvironment: "development",
+        environments: { development: { filesVersion: "1" } },
+      };
       await fs.outputJSON(localDir.absolute(".gadget/sync.json"), syncJson, { spaces: 2 });
     }
   }
diff --git a/spec/commands/sync.spec.ts b/spec/commands/sync.spec.ts
index 82c1b33f5..a3235934e 100644
--- a/spec/commands/sync.spec.ts
+++ b/spec/commands/sync.spec.ts
@@ -77,7 +77,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           "file.txt": "file v2",
         },
       }
@@ -113,7 +113,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "file.txt": "file v3",
         },
       }
@@ -153,7 +153,7 @@ describe("sync", () => {
           ".gadget/": "",
           ".gadget/backup/": "",
           ".gadget/backup/file.txt": "file v3",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"4\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"4\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"4\\"}}}",
         },
       }
     `);
@@ -197,7 +197,7 @@ describe("sync", () => {
           ".gadget/": "",
           ".gadget/backup/": "",
           ".gadget/backup/file.txt": "file v3",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"5\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"5\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"5\\"}}}",
           "directory/": "",
         },
       }
@@ -245,7 +245,7 @@ describe("sync", () => {
           ".gadget/backup/": "",
           ".gadget/backup/directory/": "",
           ".gadget/backup/file.txt": "file v3",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"6\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"6\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"6\\"}}}",
         },
       }
     `);
@@ -316,7 +316,7 @@ describe("sync", () => {
           ".gadget/backup/": "",
           ".gadget/backup/directory/": "",
           ".gadget/backup/file.txt": "file v3",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"7\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"7\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"7\\"}}}",
           "file1.txt": "file1.txt",
           "file10.txt": "file10.txt",
           "file2.txt": "file2.txt",
@@ -440,7 +440,7 @@ describe("sync", () => {
           ".gadget/backup/": "",
           ".gadget/backup/directory/": "",
           ".gadget/backup/file.txt": "file v3",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"7\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"7\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"7\\"}}}",
           "file1.txt": "file1.txt",
           "file10.txt": "file10.txt",
           "file2.txt": "file2.txt",
@@ -576,7 +576,7 @@ describe("sync", () => {
           ".gadget/backup/": "",
           ".gadget/backup/directory/": "",
           ".gadget/backup/file.txt": "file v3",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"7\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"7\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"7\\"}}}",
           "file.js": "file v2",
           "file1.txt": "file1.txt",
           "file10.txt": "file10.txt",
@@ -639,7 +639,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           ".ignore": "**/tmp",
         },
       }
@@ -680,7 +680,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           ".ignore": "**/tmp",
         },
       }
@@ -712,7 +712,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           "file.txt": "file v2",
         },
       }
@@ -742,7 +742,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "file.txt": "file v3",
         },
       }
@@ -776,7 +776,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"4\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"4\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"4\\"}}}",
           "renamed-file.txt": "file v3",
         },
       }
@@ -812,7 +812,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"5\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"5\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"5\\"}}}",
         },
       }
     `);
@@ -852,7 +852,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"6\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"6\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"6\\"}}}",
           "directory/": "",
         },
       }
@@ -897,7 +897,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"7\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"7\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"7\\"}}}",
           "renamed-directory/": "",
         },
       }
@@ -944,7 +944,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"8\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"8\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"8\\"}}}",
         },
       }
     `);
@@ -1020,7 +1020,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"9\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"9\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"9\\"}}}",
           "file1.txt": "file1.txt",
           "file10.txt": "file10.txt",
           "file2.txt": "file2.txt",
@@ -1065,7 +1065,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           "file.txt": "v10",
         },
       }
@@ -1131,7 +1131,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"1\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"1\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"1\\"}}}",
           ".ignore": "**/tmp",
           "tmp/": "",
           "tmp/file1.txt": "file1.txt",
@@ -1176,7 +1176,7 @@ describe("sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           ".ignore": "# watch it all",
         },
       }
diff --git a/spec/services/filesync/filesync.spec.ts b/spec/services/filesync/filesync.spec.ts
index 279fc5f5b..917b26241 100644
--- a/spec/services/filesync/filesync.spec.ts
+++ b/spec/services/filesync/filesync.spec.ts
@@ -48,7 +48,14 @@ describe("FileSync.init", () => {
   });
 
   it("loads state from .gadget/sync.json", async () => {
-    const state = { app: testApp.slug, environment: "development", filesVersion: "77", mtime: 1658153625236 };
+    const state = {
+      app: testApp.slug,
+      filesVersion: "77",
+      currentEnvironment: "development",
+      environments: {
+        development: { filesVersion: "77" },
+      },
+    };
     await fs.outputJSON(appDirPath(".gadget/sync.json"), state);
 
     const filesync = await FileSync.init(makeContext({ parse: args, argv: ["sync", appDir, "--app", testApp.slug] }));
@@ -58,20 +65,45 @@ describe("FileSync.init", () => {
   });
 
   it("loads state from .gadget/sync.json and sets environment to `development` if it's missing", async () => {
-    const state = { app: testApp.slug, filesVersion: "77", mtime: 1658153625236 };
+    const state = { app: testApp.slug, filesVersion: "77" };
     await fs.outputJSON(appDirPath(".gadget/sync.json"), state);
 
     const filesync = await FileSync.init(makeContext({ parse: args, argv: ["sync", appDir, "--app", testApp.slug] }));
 
     // @ts-expect-error _syncJson is private
-    expect(filesync._syncJson).toEqual({ ...state, environment: "development" });
+    expect(filesync._syncJson).toEqual({
+      ...state,
+      currentEnvironment: "development",
+      environments: { development: { filesVersion: "77" } },
+    });
+  });
+
+  it("loads state from .gadget/sync.json and ignores mtime if it exists", async () => {
+    const state = { app: testApp.slug, filesVersion: "77" };
+    await fs.outputJSON(appDirPath(".gadget/sync.json"), { ...state, mtime: "8888584595" });
+
+    const filesync = await FileSync.init(makeContext({ parse: args, argv: ["sync", appDir, "--app", testApp.slug] }));
+
+    // @ts-expect-error _syncJson is private
+    expect(filesync._syncJson).toEqual({
+      ...state,
+      currentEnvironment: "development",
+      environments: { development: { filesVersion: "77" } },
+    });
   });
 
   it("uses default state if .gadget/sync.json does not exist and `dir` is empty", async () => {
     const filesync = await FileSync.init(makeContext({ parse: args, argv: ["sync", appDir, "--app", testApp.slug] }));
 
     // @ts-expect-error _syncJson is private
-    expect(filesync._syncJson).toEqual({ app: "test", environment: "development", filesVersion: "0", mtime: 0 });
+    expect(filesync._syncJson).toEqual({
+      app: "test",
+      filesVersion: "0",
+      currentEnvironment: "development",
+      environments: {
+        development: { filesVersion: "0" },
+      },
+    });
   });
 
   it("throws InvalidSyncFileError if .gadget/sync.json does not exist and `dir` is not empty", async () => {
@@ -93,12 +125,22 @@ describe("FileSync.init", () => {
 
   it("does not throw InvalidSyncFileError if .gadget/sync.json is invalid and `--force` is passed", async () => {
     // has trailing comma
-    await fs.outputFile(appDirPath(".gadget/sync.json"), '{"app":"test","filesVersion":"77","mtime":1658153625236,}');
+    await fs.outputFile(
+      appDirPath(".gadget/sync.json"),
+      '{"app":"test","filesVersion":"77", "currentEnvironment": "development", "environments": {"development": {"filesVersion": "77"}},}',
+    );
 
     const filesync = await FileSync.init(makeContext({ parse: args, argv: ["sync", appDir, "--app", testApp.slug, "--force"] }));
 
     // @ts-expect-error _syncJson is private
-    expect(filesync._syncJson).toEqual({ app: testApp.slug, environment: "development", filesVersion: "0", mtime: 0 });
+    expect(filesync._syncJson).toEqual({
+      app: testApp.slug,
+      currentEnvironment: "development",
+      filesVersion: "0",
+      environments: {
+        development: { filesVersion: "0" },
+      },
+    });
   });
 
   it("throws ArgError if the `--app` arg is passed a slug that does not exist within the user's available apps", async () => {
@@ -143,9 +185,11 @@ describe("FileSync.init", () => {
   it("does not throw ArgError if the `--environment` flag is passed a different environment than the one in .gadget/sync.json", async () => {
     await fs.outputJson(appDirPath(".gadget/sync.json"), {
       app: multiEnvironmentTestApp.slug,
-      environment: "development",
+      currentEnvironment: "development",
       filesVersion: "0",
-      mtime: 0,
+      environments: {
+        development: { filesVersion: "0" },
+      },
     });
 
     const filesync = await FileSync.init(
@@ -158,27 +202,45 @@ describe("FileSync.init", () => {
     // @ts-expect-error _syncJson is private
     expect(filesync._syncJson).toEqual({
       app: multiEnvironmentTestApp.slug,
-      environment: "other-environment-development",
+      currentEnvironment: "other-environment-development",
       filesVersion: "0",
-      mtime: 0,
+      environments: {
+        development: { filesVersion: "0" },
+      },
     });
   });
 
   it("does not throw ArgError if the `--app` flag is passed a different app name than the one in .gadget/sync.json and `--force` is passed", async () => {
-    await fs.outputJson(appDirPath(".gadget/sync.json"), { app: "not-test", filesVersion: "77", mtime: 1658153625236 });
+    await fs.outputJson(appDirPath(".gadget/sync.json"), {
+      app: "not-test",
+      currentEnvironment: "development",
+      filesVersion: "77",
+      environments: {
+        development: { filesVersion: "77" },
+      },
+    });
 
     const filesync = await FileSync.init(makeContext({ parse: args, argv: ["sync", appDir, "--app", testApp.slug, "--force"] }));
 
     // @ts-expect-error _syncJson is private
-    expect(filesync._syncJson).toEqual({ app: testApp.slug, environment: "development", filesVersion: "0", mtime: 0 });
+    expect(filesync._syncJson).toEqual({
+      app: testApp.slug,
+      filesVersion: "0",
+      currentEnvironment: "development",
+      environments: { development: { filesVersion: "0" } },
+    });
   });
 
   it("does not throw ArgError if the `--environment` flag is passed a different environment than the one in .gadget/sync.json and `--force` is passed", async () => {
     await fs.outputJson(appDirPath(".gadget/sync.json"), {
-      app: "test",
-      environment: "development",
-      filesVersion: "0",
-      mtime: 0,
+      app: multiEnvironmentTestApp.slug,
+      filesVersion: "77",
+      currentEnvironment: "development",
+      environments: {
+        development: {
+          filesVersion: "77",
+        },
+      },
     });
 
     const filesync = await FileSync.init(
@@ -191,9 +253,13 @@ describe("FileSync.init", () => {
     // @ts-expect-error _syncJson is private
     expect(filesync._syncJson).toEqual({
       app: multiEnvironmentTestApp.slug,
-      environment: "cool-environment-development",
-      filesVersion: "0",
-      mtime: 0,
+      currentEnvironment: "cool-environment-development",
+      filesVersion: "77",
+      environments: {
+        development: {
+          filesVersion: "77",
+        },
+      },
     });
   });
 });
@@ -676,7 +742,7 @@ describe("FileSync.sendChangesToGadget", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "gadget.txt": "// gadget",
           "local.txt": "// local",
         },
@@ -742,7 +808,7 @@ describe("FileSync.sendChangesToGadget", () => {
         "localDir": {
           ".gadget/": "",
           ".gadget/client.js": "// client",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"4\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"4\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"4\\"}}}",
           "gadget.txt": "// gadget",
           "local.txt": "// local",
         },
@@ -784,7 +850,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"1\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"1\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"1\\"}}}",
           "foo.js": "// foo",
         },
       }
@@ -827,7 +893,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"1\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"1\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"1\\"}}}",
           ".ignore": "foo.js",
           "foo.js": "// foo (local)",
         },
@@ -881,7 +947,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo",
           "gadget-file.js": "// gadget",
           "local-file.js": "// local",
@@ -921,7 +987,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"1\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"1\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"1\\"}}}",
           "foo.js": "foo (local)",
         },
       }
@@ -967,7 +1033,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (local)",
         },
       }
@@ -1014,7 +1080,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (local)",
         },
       }
@@ -1069,7 +1135,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (local)",
           "gadget-file.js": "// gadget",
           "local-file.js": "// local",
@@ -1125,7 +1191,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (local)",
           "gadget-file.js": "// gadget",
           "local-file.js": "// local",
@@ -1171,7 +1237,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           "foo.js": "// foo (gadget)",
         },
       }
@@ -1214,7 +1280,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           "foo.js": "// foo (gadget)",
         },
       }
@@ -1269,7 +1335,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (gadget)",
           "gadget-file.js": "// gadget",
           "local-file.js": "// local",
@@ -1326,7 +1392,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (gadget)",
           "gadget-file.js": "// gadget",
           "local-file.js": "// local",
@@ -1382,7 +1448,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (gadget)",
           "gadget-file.js": "// gadget",
           "local-file.js": "// local",
@@ -1427,7 +1493,7 @@ describe("FileSync.sync", () => {
         "localDir": {
           ".gadget/": "",
           ".gadget/client.js": "// client (gadget)",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
         },
       }
     `);
@@ -1482,7 +1548,7 @@ describe("FileSync.sync", () => {
         "localDir": {
           ".gadget/": "",
           ".gadget/client.js": "// client (gadget)",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "foo.js": "// foo (local)",
         },
       }
@@ -1519,7 +1585,7 @@ describe("FileSync.sync", () => {
         "localDir": {
           ".gadget/": "",
           ".gadget/client.js": "// client",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"1\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"1\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"1\\"}}}",
         },
       }
     `);
@@ -1576,7 +1642,7 @@ describe("FileSync.sync", () => {
           ".gadget/": "",
           ".gadget/client.js": "// client",
           ".gadget/server.js": "// server",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"2\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"2\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"2\\"}}}",
           "gadget-file.js": "// gadget",
           "local-file.js": "// local",
         },
@@ -1630,7 +1696,7 @@ describe("FileSync.sync", () => {
         },
         "localDir": {
           ".gadget/": "",
-          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"environment\\":\\"development\\",\\"filesVersion\\":\\"3\\"}",
+          ".gadget/sync.json": "{\\"app\\":\\"test\\",\\"filesVersion\\":\\"3\\",\\"currentEnvironment\\":\\"development\\",\\"environments\\":{\\"development\\":{\\"filesVersion\\":\\"3\\"}}}",
           "gadget.txt": "// gadget",
           "local.txt": "// local",
         },
diff --git a/src/services/filesync/filesync.ts b/src/services/filesync/filesync.ts
index d0d8ce687..33c36958f 100644
--- a/src/services/filesync/filesync.ts
+++ b/src/services/filesync/filesync.ts
@@ -84,7 +84,12 @@ export class FileSync {
      *
      * This is persisted to `.gadget/sync.json` within the {@linkcode directory}.
      */
-    private _syncJson: { app: string; environment: string; environments: Record<string, { filesVersion: string }> },
+    private _syncJson: {
+      app: string;
+      filesVersion: string;
+      currentEnvironment: string;
+      environments: Record<string, { filesVersion: string }>;
+    },
   ) {
     this.ctx = ctx.child({
       fields: () => ({ filesync: { directory: this.directory.path, filesVersion: this.filesVersion } }),
@@ -156,16 +161,18 @@ export class FileSync {
         return z
           .object({
             app: z.string(),
-            environment: z
+            filesVersion: z
               .string()
               .nullish()
-              .transform((x) => x?.toLowerCase() ?? "development"), // old sync.json environment's may be null/undefined so default to development
-            filesVersion: z.string(),
-            mtime: z.number(),
+              .transform((x) => x ?? "0"), // Legacy support for old sync.json files
+            currentEnvironment: z
+              .string()
+              .nullish()
+              .transform((x) => x ?? "development"), // New support for multi environment, but old sync.json files don't have this
             environments: z
               .record(z.object({ filesVersion: z.string() }))
               .nullish()
-              .transform((value, ctx) => value ?? { development: { filesVersion: "0" } }),
+              .transform((value, _ctx) => value ?? { development: { filesVersion: "0" } }),
           })
           .parse(json);
       })
@@ -173,7 +180,7 @@ export class FileSync {
 
     // Basically a hack for reverse compatibility with old sync.json files
     const devEnvrionmentState = state?.environments["development"];
-    if (devEnvrionmentState && devEnvrionmentState.filesVersion !== state.filesVersion) {
+    if (devEnvrionmentState && state.filesVersion && devEnvrionmentState.filesVersion !== state.filesVersion) {
       // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
       state.environments["development"]!.filesVersion = state.filesVersion;
     }
@@ -212,7 +219,7 @@ export class FileSync {
       );
     }
 
-    let environment = ctx.args["--environment"]?.toLowerCase() || state?.environment?.toLowerCase();
+    let environment = ctx.args["--environment"]?.toLowerCase() || state?.currentEnvironment?.toLowerCase();
     const filteredSelectableEnvironments = app.environments.filter((x) => x.type.toLowerCase() !== "production");
 
     if (app.multiEnvironmentEnabled) {
@@ -244,7 +251,7 @@ export class FileSync {
           `.concat(`  • ${similarEnvironments.join("\n  • ")}`),
         );
       }
-    } else if (environment) {
+    } else if (ctx.args["--environment"]?.toLowerCase()) {
       // multi environment is not enabled but the user specified an environment
       throw new ArgError(
         sprint`
@@ -269,7 +276,8 @@ export class FileSync {
         // either way, create a fresh .gadget/sync.json file
         return new FileSync(ctx, directory, app, environment, {
           app: app.slug,
-          environment,
+          filesVersion: "0",
+          currentEnvironment: environment,
           environments: {
             [environment]: { filesVersion: "0" },
           },
@@ -283,14 +291,20 @@ export class FileSync {
     // the .gadget/sync.json file exists
     if (state.app === app.slug) {
       // the .gadget/sync.json file is for the same app
-      return new FileSync(ctx, directory, app, environment, { ...state, environment });
+      return new FileSync(ctx, directory, app, environment, { ...state, currentEnvironment: environment });
     }
 
     // the .gadget/sync.json file is for a different app or environment
     if (ctx.args["--force"]) {
       // the user passed --force, so use the app they specified and overwrite everything
-      const { environments } = state;
-      return new FileSync(ctx, directory, app, environment, { app: app.slug, environment, environments });
+      return new FileSync(ctx, directory, app, environment, {
+        app: app.slug,
+        filesVersion: "0",
+        currentEnvironment: environment,
+        environments: {
+          [environment]: { filesVersion: "0" },
+        },
+      });
     }
 
     // the user didn't pass --force, so throw an error
@@ -301,7 +315,7 @@ export class FileSync {
 
         However, that directory has already been synced with this app:
 
-          {dim ${state.app}} {dim ({red ${state.environment}})}
+          {dim ${state.app}} {dim ({red ${state.currentEnvironment}})}
 
         If you're sure that you want to sync:
 
@@ -785,7 +799,11 @@ export class FileSync {
    * Updates {@linkcode _syncJson} and saves it to `.gadget/sync.json`.
    */
   private async _save(filesVersion: string | bigint): Promise<void> {
-    this._syncJson = { ...this._syncJson, mtime: Date.now() + 1, filesVersion: String(filesVersion) };
+    this._syncJson = {
+      ...this._syncJson,
+      filesVersion: String(filesVersion),
+      environments: { ...this._syncJson.environments, [this.environment]: { filesVersion: String(filesVersion) } },
+    };
     this.ctx.log.debug("saving .gadget/sync.json");
     await fs.outputJSON(this.directory.absolute(".gadget/sync.json"), this._syncJson, { spaces: 2 });
   }