diff --git a/src/roe/__init__.py b/src/roe/__init__.py
index ece5b2c..4bd9244 100644
--- a/src/roe/__init__.py
+++ b/src/roe/__init__.py
@@ -30,6 +30,7 @@
     ForbiddenError,
     InsufficientCreditsError,
     NotFoundError,
+    RateLimitError,
     RoeAPIException,
     ServerError,
 )
@@ -58,5 +59,6 @@
     "ForbiddenError",
     "InsufficientCreditsError",
     "NotFoundError",
+    "RateLimitError",
     "ServerError",
 ]
diff --git a/src/roe/api/policies.py b/src/roe/api/policies.py
index f02c177..2d18a7d 100644
--- a/src/roe/api/policies.py
+++ b/src/roe/api/policies.py
@@ -43,13 +43,9 @@
 from roe.utils.generated_request import request_json, request_raw
 
 
-_ZERO_UUID = "00000000-0000-0000-0000-000000000000"
-
-
 def _normalize_policy_version_wire(data: dict[str, Any]) -> dict[str, Any]:
     normalized = dict(data)
-    if normalized.get("base_version_id") is None:
-        normalized["base_version_id"] = _ZERO_UUID
+    normalized.setdefault("base_version_id", None)
     return normalized
 
 
diff --git a/src/roe/exceptions.py b/src/roe/exceptions.py
index ef91446..07b6356 100644
--- a/src/roe/exceptions.py
+++ b/src/roe/exceptions.py
@@ -62,6 +62,12 @@ class NotFoundError(RoeAPIException):
     pass
 
 
+class RateLimitError(RoeAPIException):
+    """429 Too Many Requests - Rate limit exceeded."""
+
+    pass
+
+
 class ServerError(RoeAPIException):
     """500+ Server Error - Internal server errors."""
 
@@ -76,6 +82,7 @@ def get_exception_for_status_code(status_code: int) -> type[RoeAPIException]:
         402: InsufficientCreditsError,
         403: ForbiddenError,
         404: NotFoundError,
+        429: RateLimitError,
     }
 
     if status_code in exception_map:
@@ -115,6 +122,10 @@ def translate_response(response: Any) -> None:
 
     if isinstance(body, dict):
         message = body.get("detail") or body.get("error") or body.get("message")
+        if isinstance(message, list):
+            message = "; ".join(str(e) for e in message)
+        elif message and not isinstance(message, str):
+            message = str(message)
         if not message:
             for value in body.values():
                 if isinstance(value, list) and value:
diff --git a/src/roe/models/file.py b/src/roe/models/file.py
index ea1bcd6..b365cb0 100644
--- a/src/roe/models/file.py
+++ b/src/roe/models/file.py
@@ -4,21 +4,23 @@
 import os
 from typing import BinaryIO
 
-from pydantic import BaseModel, Field, model_validator
+from pydantic import BaseModel, ConfigDict, Field, SkipValidation, model_validator
 
 
 class FileUpload(BaseModel):
     """Helper class for explicit file uploads with metadata."""
 
     path: str | None = Field(default=None, description="File path to upload")
-    file_obj: BinaryIO | None = Field(default=None, description="File object to upload")
+    # SkipValidation: real file objects aren't isinstance(BinaryIO), so validation rejects them.
+    file_obj: SkipValidation[BinaryIO] | None = Field(
+        default=None, description="File object to upload"
+    )
     filename: str | None = Field(default=None, description="Override filename")
     mime_type: str | None = Field(
         default=None, description="MIME type (auto-detected if not provided)"
     )
 
-    class Config:
-        arbitrary_types_allowed = True
+    model_config = ConfigDict(arbitrary_types_allowed=True)
 
     @model_validator(mode="after")
     def validate_file_source(self):
diff --git a/src/roe/utils/transport.py b/src/roe/utils/transport.py
index d18fce6..1c429e6 100644
--- a/src/roe/utils/transport.py
+++ b/src/roe/utils/transport.py
@@ -1,6 +1,7 @@
 """Custom httpx transport with retry policy for the Roe SDK.
 
-Retries failed requests with exponential backoff (capped at ~10 seconds):
+Retries failed requests with exponential backoff (capped at ~10 seconds, or
+longer when a 429/503 sends an integer ``Retry-After``, up to 60 seconds):
 
 - Transport errors: ``httpx.TransportError`` (disconnects, timeouts, etc.).
 - HTTP statuses: ``5xx``, ``408``, ``429``.
@@ -32,6 +33,13 @@ def _should_retry_status(status_code: int) -> bool:
     return status_code >= 500 or status_code in (408, 429)
 
 
+def _retry_after_seconds(response: httpx.Response) -> int:
+    value = response.headers.get("retry-after", "")
+    if response.status_code in (429, 503) and value.isdecimal():
+        return min(int(value), 60)
+    return 0
+
+
 class RoeRetryTransport(httpx.HTTPTransport):
     """httpx transport with configurable retries aligned with TS and Go SDKs."""
 
@@ -68,7 +76,7 @@ def handle_request(self, request: httpx.Request) -> httpx.Response:
             ):
                 return response
 
-            wait_time = min(2**attempt, 10)
+            wait_time = max(min(2**attempt, 10), _retry_after_seconds(response))
             logger.warning(
                 "Roe API returned %d for %s %s, retrying in %ds (attempt %d/%d)",
                 response.status_code,
diff --git a/tests/unit/test_file_upload.py b/tests/unit/test_file_upload.py
new file mode 100644
index 0000000..6994464
--- /dev/null
+++ b/tests/unit/test_file_upload.py
@@ -0,0 +1,27 @@
+import io
+import subprocess
+import sys
+
+from roe.models.file import FileUpload
+
+
+def test_file_upload_import_emits_no_deprecation_warning():
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-W",
+            "error::DeprecationWarning",
+            "-c",
+            "import roe.models.file",
+        ],
+        capture_output=True,
+        text=True,
+    )
+    assert result.returncode == 0, result.stderr
+
+
+def test_file_upload_accepts_file_object():
+    buf = io.BytesIO(b"data")
+    upload = FileUpload(file_obj=buf, filename="a.txt")
+
+    assert upload.to_multipart_tuple() == ("a.txt", buf, "text/plain")
diff --git a/tests/unit/test_policies_wrapper_transport.py b/tests/unit/test_policies_wrapper_transport.py
index 4aa46f2..a1fed37 100644
--- a/tests/unit/test_policies_wrapper_transport.py
+++ b/tests/unit/test_policies_wrapper_transport.py
@@ -44,3 +44,21 @@ def test_policy_replace_uses_put_with_org_query_and_model_body():
     assert kwargs["params"] == {"organization_id": ORG_ID}
     assert kwargs["json"] == {"name": "Policy", "description": "desc"}
     assert result.id == UUID(POLICY_ID)
+
+
+def test_policy_version_without_base_version_keeps_none():
+    version = {
+        "id": "00000000-0000-0000-0000-000000000555",
+        "version_name": "v1",
+        "content": {},
+        "created_at": "2025-01-01T00:00:00Z",
+        "updated_at": "2025-01-01T00:00:00Z",
+        "policy": _update_policy_json(),
+        "created_by": {"id": 1, "email": "a@b.c", "display_name": "A"},
+        "base_version_id": None,
+    }
+    api, _ = _api(httpx.Response(200, json=version))
+
+    result = api.versions.retrieve(POLICY_ID, version["id"])
+
+    assert result.base_version_id is None
diff --git a/tests/unit/test_translate_response.py b/tests/unit/test_translate_response.py
index 9f99e31..f7719e2 100644
--- a/tests/unit/test_translate_response.py
+++ b/tests/unit/test_translate_response.py
@@ -17,6 +17,7 @@
     ForbiddenError,
     InsufficientCreditsError,
     NotFoundError,
+    RateLimitError,
     RoeAPIException,
     ServerError,
     translate_response,
@@ -40,7 +41,7 @@ def test_2xx_is_noop():
         (402, InsufficientCreditsError),
         (403, ForbiddenError),
         (404, NotFoundError),
-        (429, RoeAPIException),
+        (429, RateLimitError),
         (500, ServerError),
         (502, ServerError),
     ],
@@ -66,6 +67,19 @@ def test_list_body_joined_as_message():
     assert exc_info.value.response is None
 
 
+@pytest.mark.parametrize(
+    "content,expected",
+    [
+        (b'{"detail": ["a", "b"]}', "a; b"),
+        (b'{"error": {"code": "bad"}}', "{'code': 'bad'}"),
+    ],
+)
+def test_non_string_detail_becomes_string_message(content, expected):
+    with pytest.raises(BadRequestError) as exc_info:
+        translate_response(_resp(400, content))
+    assert exc_info.value.message == expected
+
+
 def test_non_json_body_falls_back_to_status_snippet():
     with pytest.raises(NotFoundError) as exc_info:
         translate_response(_resp(404, b"<html>not found</html>"))
diff --git a/tests/unit/test_transport.py b/tests/unit/test_transport.py
new file mode 100644
index 0000000..f74b6ff
--- /dev/null
+++ b/tests/unit/test_transport.py
@@ -0,0 +1,30 @@
+import httpx
+import pytest
+
+from roe.utils import transport
+from roe.utils.transport import RoeRetryTransport
+
+
+@pytest.mark.parametrize(
+    ("status", "retry_after", "expected_sleep"),
+    [(429, "5", 5), (503, "120", 60), (429, "Wed, 21 Oct 2025 07:28:00 GMT", 1)],
+)
+def test_retry_waits_for_retry_after_seconds(
+    monkeypatch, status, retry_after, expected_sleep
+):
+    responses = [
+        httpx.Response(status, headers={"Retry-After": retry_after}),
+        httpx.Response(200),
+    ]
+    sleeps = []
+    monkeypatch.setattr(
+        httpx.HTTPTransport, "handle_request", lambda self, req: responses.pop(0)
+    )
+    monkeypatch.setattr(transport.time, "sleep", sleeps.append)
+
+    response = RoeRetryTransport().handle_request(
+        httpx.Request("GET", "https://example.com")
+    )
+
+    assert response.status_code == 200
+    assert sleeps == [expected_sleep]