diff --git a/tools/bundler.js b/tools/bundler.js
index 52f1fe5478..1db6635526 100644
--- a/tools/bundler.js
+++ b/tools/bundler.js
@@ -2,7 +2,7 @@
 //
 // /star.json
 //
-//  - format: "site-archive-1" for this version
+//  - format: "site-archive-pre1" for this version
 //
 //  - builtBy: human readable banner (eg, "Meteor 0.6.0")
 //
@@ -54,7 +54,7 @@
 //
 // /program.json
 //
-//  - format: "browser-program-1" for this version
+//  - format: "browser-program-pre1" for this version
 //
 //  - page: path to the template for the HTML to serve when a browser
 //    loads a page that is part of the application. In the file
@@ -138,7 +138,7 @@
 // == Format of a program that is to be used as a plugin ==
 //
 // /program.json:
-//  - format: "javascript-image-1" for this version
+//  - format: "javascript-image-pre1" for this version
 //  - arch: the architecture that this build requires
 //  - load: array with each item describing a JS file to load, in load order:
 //    - path: path of file, relative to program.json
@@ -724,7 +724,7 @@ _.extend(ClientTarget.prototype, {
 
     // Control file
     builder.writeJson('program.json', {
-      format: "browser-program-1",
+      format: "browser-program-pre1",
       manifest: manifest,
       page: 'app.html',
 
@@ -894,22 +894,22 @@ _.extend(JsImage.prototype, {
     // Control file
     builder.writeJson('program.json', {
       load: load,
-      format: "javascript-image-1",
+      format: "javascript-image-pre1",
       arch: self.arch
     });
     return "program.json";
   }
 });
 
-// Create a JsImage by loading a bundle of format 'javascript-image-1'
-// from disk (eg, previously written out with write().) `dir` is the
-// path to the control file.
+// Create a JsImage by loading a bundle of format
+// 'javascript-image-pre1' from disk (eg, previously written out with
+// write().) `dir` is the path to the control file.
 JsImage.readFromDisk = function (controlFilePath) {
   var ret = new JsImage;
   var json = JSON.parse(fs.readFileSync(controlFilePath));
   var dir = path.dirname(controlFilePath);
 
-  if (json.format !== "javascript-image-1")
+  if (json.format !== "javascript-image-pre1")
     throw new Error("Unsupported plugin format: " +
                     JSON.stringify(json.format));
 
@@ -1103,7 +1103,7 @@ var writeSiteArchive = function (targets, outputPath, options) {
 
   try {
     var json = {
-      format: "site-archive-1",
+      format: "site-archive-pre1",
       builtBy: options.builtBy,
       programs: []
     };
diff --git a/tools/packages.js b/tools/packages.js
index 5e2a74be4e..53960808e3 100644
--- a/tools/packages.js
+++ b/tools/packages.js
@@ -1574,7 +1574,7 @@ _.extend(Package.prototype, {
     var mainJson =
       JSON.parse(fs.readFileSync(path.join(dir, 'unipackage.json')));
 
-    if (mainJson.format !== "unipackage-1")
+    if (mainJson.format !== "unipackage-pre1")
       throw new Error("Unsupported unipackage format: " +
                       JSON.stringify(mainJson.format));
 
@@ -1666,7 +1666,7 @@ _.extend(Package.prototype, {
         fs.readFileSync(path.join(dir, sliceMeta.path)));
       var sliceBasePath = path.dirname(path.join(dir, sliceMeta.path));
 
-      if (sliceJson.format!== "unipackage-slice-1")
+      if (sliceJson.format!== "unipackage-slice-pre1")
         throw new Error("Unsupported unipackage slice format: " +
                         JSON.stringify(sliceJson.format));
 
@@ -1752,7 +1752,7 @@ _.extend(Package.prototype, {
     try {
 
       var mainJson = {
-        format: "unipackage-1",
+        format: "unipackage-pre1",
         summary: self.metadata.summary,
         internal: self.metadata.internal,
         slices: [],
@@ -1801,7 +1801,7 @@ _.extend(Package.prototype, {
 
         // Construct slice metadata
         var sliceJson = {
-          format: "unipackage-slice-1",
+          format: "unipackage-slice-pre1",
           exports: slice.exports,
           uses: _.map(slice.uses, function (u) {
             var specParts = u.spec.split('.');
diff --git a/tools/server/boot.js b/tools/server/boot.js
index 8a53d1f0ff..5f2d272a1b 100644
--- a/tools/server/boot.js
+++ b/tools/server/boot.js
@@ -153,7 +153,7 @@ var run = function () {
   var clientDir = path.dirname(clientJsonPath);
   var clientJson = JSON.parse(fs.readFileSync(clientJsonPath, 'utf8'));
 
-  if (clientJson.format !== "browser-program-1")
+  if (clientJson.format !== "browser-program-pre1")
     throw new Error("Unsupported format for client assets: " +
                     JSON.stringify(clientJson.format));