diff --git a/manifest_xml.py b/manifest_xml.py
index 3c43295e3..db7a92865 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -768,8 +768,11 @@ https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
 
   @property
   def is_multimanifest(self):
-    """Whether this is a multimanifest checkout"""
-    return bool(self.outer_client.submanifests)
+    """Whether this is a multimanifest checkout.
+
+    This is safe to use as long as the outermost manifest XML has been parsed.
+    """
+    return bool(self._outer_client._submanifests)
 
   @property
   def is_submanifest(self):
@@ -1679,7 +1682,7 @@ https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
       # We allow people to mix git worktrees & non-git worktrees for now.
       # This allows for in situ migration of repo clients.
       if os.path.exists(gitdir) or not self.UseGitWorktrees:
-        objdir = os.path.join(self.subdir, 'project-objects', namepath)
+        objdir = os.path.join(self.repodir, 'project-objects', namepath)
       else:
         use_git_worktrees = True
         gitdir = os.path.join(self.repodir, 'worktrees', namepath)
diff --git a/project.py b/project.py
index b7ed6f336..faa6b32b1 100644
--- a/project.py
+++ b/project.py
@@ -49,6 +49,9 @@ MAXIMUM_RETRY_SLEEP_SEC = 3600.0
 # +-10% random jitter is added to each Fetches retry sleep duration.
 RETRY_JITTER_PERCENT = 0.1
 
+# Whether to use alternates.
+# TODO(vapier): Remove knob once behavior is verified.
+_ALTERNATES = os.environ.get('REPO_USE_ALTERNATES') == '1'
 
 def _lwrite(path, content):
   lock = '%s.lock' % path
@@ -460,7 +463,7 @@ class RemoteSpec(object):
 
 class Project(object):
   # These objects can be shared between several working trees.
-  shareable_dirs = ['hooks', 'objects', 'rr-cache']
+  shareable_dirs = ['hooks', 'rr-cache']
 
   def __init__(self,
                manifest,
@@ -1143,6 +1146,17 @@ class Project(object):
       self._UpdateHooks(quiet=quiet)
     self._InitRemote()
 
+    if _ALTERNATES or self.manifest.is_multimanifest:
+      # If gitdir/objects is a symlink, migrate it from the old layout.
+      gitdir_objects = os.path.join(self.gitdir, 'objects')
+      if platform_utils.islink(gitdir_objects):
+        platform_utils.remove(gitdir_objects, missing_ok=True)
+      gitdir_alt = os.path.join(self.gitdir, 'objects/info/alternates')
+      if not os.path.exists(gitdir_alt):
+        os.makedirs(os.path.dirname(gitdir_alt), exist_ok=True)
+        _lwrite(gitdir_alt, os.path.join(
+            os.path.relpath(self.objdir, gitdir_objects), 'objects') + '\n')
+
     if is_new:
       alt = os.path.join(self.objdir, 'objects/info/alternates')
       try: