@@ -45,6 +45,14 @@ fallbacks.
 
 ## Index and object metadata lifecycle
 
+`git.GitDB` and `git.db.GitDB` remain compatibility aliases for
+`GitCmdObjectDB`, so legacy `Repo(..., odbt=GitDB)` selectors use the same
+managed backend. Aider 0.86.2 uses that selector for every repository open.
+This does not restore gitdb's Python object database or its specialized APIs.
+Object queries continue through `object_data()` and the supported
+`Repository.try_find_header()`/`find_object()` APIs, with the existing large-object
+and diagnostic CLI fallbacks. Storage uses the existing `hash_object` dispatch.
+
 `IndexFile` queries immutable entry records; it does not retain a parsed index.
 The compatibility `entries` property projects those queries into a read-only
 snapshot keyed by path and stage, preserving readers in dlt and Renku. It uses
 
@@ -54,9 +54,11 @@ API changes
 * ``GitCmdObjectDB`` no longer inherits ``LooseObjectDB``. Its object reads,
   writes, existence checks, and enumeration use Git, including packed objects.
   Precompressed input streams and custom object-output writers are unsupported.
-  ``GitDB`` exports and backend selection are removed. ``odbt`` accepts only
-  ``GitCmdObjectDB`` and its subclasses, rejecting unsupported types before
-  initialization or cloning. Remove ``odbt=GitDB`` or select ``GitCmdObjectDB``.
+  ``GitDB`` remains exported as a compatibility alias for ``GitCmdObjectDB``;
+  ``odbt=GitDB`` selects the same managed Git/Gix backend. It no longer selects
+  gitdb's Python storage implementation or supports that implementation's
+  specialized interfaces. ``odbt`` accepts ``GitCmdObjectDB`` and its subclasses,
+  rejecting unsupported types before initialization or cloning.
   ``gitdb`` remains a dependency for shared types and utilities.
 * ``Repo.object_format`` and ``Repo.ref_format`` report Git's storage formats.
   ``Repo.alternates`` is read-only and reports effective absolute alternate
 
@@ -29,6 +29,7 @@
     "GitCommandError",
     "GitCommandNotFound",
     "GitConfigParser",
+    "GitDB",
     "GitError",
     "HEAD",
     "Head",
@@ -146,7 +147,7 @@
         DiffIndex,
         Diffable,
     )
-    from git.db import GitCmdObjectDB  # @NoMove
+    from git.db import GitCmdObjectDB, GitDB  # @NoMove
     from git.cmd import Git  # @NoMove
     from git.repo import Repo  # @NoMove
     from git.remote import FetchInfo, PushInfo, Remote, RemoteProgress  # @NoMove
 
@@ -3,7 +3,7 @@
 
 """Git's object database, accessed exclusively through the Git command."""
 
-__all__ = ["GitCmdObjectDB"]
+__all__ = ["GitCmdObjectDB", "GitDB"]
 
 import tempfile
 from typing import Iterator, TYPE_CHECKING
@@ -107,3 +107,8 @@ def partial_to_complete_sha_hex(self, partial_hexsha: str) -> bytes:
             return hex_to_bin(hexsha)
         except (GitCommandError, ValueError) as exc:
             raise BadObject(partial_hexsha) from exc
+
+
+# Preserve the public object-backend selector used by downstream applications.
+# Storage remains owned by Git/Gix; this does not restore gitdb's Python backend.
+GitDB = GitCmdObjectDB
@@ -4,9 +4,27 @@
 
 import pytest
 
+import git
+import git.db
+
 from test.lib.fixtures import fixture_repo
 
 
+@pytest.mark.parametrize("object_format", ["sha1", "sha256"])
+@pytest.mark.parametrize("ref_format", ["files", "reftable"])
+def test_legacy_gitdb_selector_uses_the_managed_object_backend(object_format, ref_format):
+    assert git.GitDB is git.db.GitDB is git.GitCmdObjectDB
+    with fixture_repo("downstream-index.sh", object_format, ref_format) as fixture:
+        with git.Repo(fixture.working_tree_dir, odbt=git.GitDB) as repo:
+            assert isinstance(repo.odb, git.GitCmdObjectDB)
+            blob = repo.head.commit.tree["tracked"]
+            assert repo.odb.has_object(blob.binsha)
+            info = repo.odb.info(blob.binsha)
+            assert info.binsha == blob.binsha
+            assert info.type == b"blob"
+            assert repo.odb.stream(blob.binsha).read() == blob.data_stream.read()
+
+
 @pytest.mark.parametrize("object_format", ["sha1", "sha256"])
 @pytest.mark.parametrize("ref_format", ["files", "reftable"])
 def test_index_entries_readers_retain_pending_and_published_snapshots(object_format, ref_format):