diff --git a/strix/interface/cloud/source_upload.py b/strix/interface/cloud/source_upload.py
index 780a8456..0c7e93ea 100644
--- a/strix/interface/cloud/source_upload.py
+++ b/strix/interface/cloud/source_upload.py
@@ -585,6 +585,21 @@ def _matches_user_pattern(relative: Path, pattern: str) -> bool:
     return posix.match(pattern) or fnmatch.fnmatch(relative_posix, pattern)
 
 
+def _is_stat_unchanged(stat_result: os.stat_result, item: SelectedFile) -> bool:
+    if (
+        not stat.S_ISREG(stat_result.st_mode)
+        or stat_result.st_size != item.size
+        or stat_result.st_dev != item.device
+        or stat_result.st_ino != item.inode
+        or stat_result.st_mtime_ns != item.mtime_ns
+    ):
+        return False
+    # On Windows (NTFS/FAT), st_ctime represents file creation time rather than
+    # POSIX inode change time, and its nanosecond timestamp can settle asynchronously
+    # after creation without any content or attribute changes.
+    return os.name == "nt" or stat_result.st_ctime_ns == item.ctime_ns
+
+
 def _write_archive(destination: Path, files: tuple[SelectedFile, ...]) -> None:
     with zipfile.ZipFile(
         destination, "w", compression=zipfile.ZIP_DEFLATED, compresslevel=6
@@ -597,14 +612,7 @@ def _write_archive(destination: Path, files: tuple[SelectedFile, ...]) -> None:
                 raise http.CloudError(f"could not safely read {item.archive_name}: {exc}") from exc
             with os.fdopen(descriptor, "rb") as source_file:
                 current = os.fstat(source_file.fileno())
-                if (
-                    not stat.S_ISREG(current.st_mode)
-                    or current.st_size != item.size
-                    or current.st_dev != item.device
-                    or current.st_ino != item.inode
-                    or current.st_mtime_ns != item.mtime_ns
-                    or current.st_ctime_ns != item.ctime_ns
-                ):
+                if not _is_stat_unchanged(current, item):
                     raise http.CloudError(
                         f"{item.archive_name} changed while the source archive was being built; "
                         "retry."
@@ -624,15 +632,7 @@ def _write_archive(destination: Path, files: tuple[SelectedFile, ...]) -> None:
                         target.write(chunk)
                         remaining -= len(chunk)
                     final = os.fstat(source_file.fileno())
-                    if (
-                        source_file.read(1)
-                        or not stat.S_ISREG(final.st_mode)
-                        or final.st_size != item.size
-                        or final.st_dev != item.device
-                        or final.st_ino != item.inode
-                        or final.st_mtime_ns != item.mtime_ns
-                        or final.st_ctime_ns != item.ctime_ns
-                    ):
+                    if source_file.read(1) or not _is_stat_unchanged(final, item):
                         raise http.CloudError(
                             f"{item.archive_name} changed while the source archive was being "
                             "built; retry."
diff --git a/tests/test_cloud_source_upload.py b/tests/test_cloud_source_upload.py
index dcd40baa..0284ebee 100644
--- a/tests/test_cloud_source_upload.py
+++ b/tests/test_cloud_source_upload.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import dataclasses
 import json
 import os
 import shutil
@@ -274,6 +275,64 @@ def test_source_archive_rejects_same_inode_same_size_change_after_review(tmp_pat
         source_upload._write_archive(tmp_path / "source.zip", manifest.files)
 
 
+def test_source_archive_ignores_windows_ctime_settling_on_unchanged_files(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    source_path = tmp_path / "app.py"
+    source_path.write_bytes(b"safe")
+    manifest = source_upload.select_source(tmp_path)
+    selected = manifest.files[0]
+
+    # Simulate a settled/drifted ctime_ns while mtime, size, device, and inode stay identical
+    drifted_selected = dataclasses.replace(selected, ctime_ns=selected.ctime_ns + 5_000_000)
+
+    # On Windows, ctime settling must NOT reject unchanged files
+    monkeypatch.setattr(os, "name", "nt")
+    archive_path = tmp_path / "source_nt.zip"
+    source_upload._write_archive(archive_path, (drifted_selected,))
+    assert archive_path.is_file()
+
+    # On non-Windows platforms, ctime change represents inode change and MUST be rejected
+    monkeypatch.setattr(os, "name", "posix")
+    with pytest.raises(http.CloudError, match="changed while the source archive was being built"):
+        source_upload._write_archive(tmp_path / "source_posix.zip", (drifted_selected,))
+
+
+def test_source_archive_still_rejects_modifications_on_windows(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setattr(os, "name", "nt")
+    source_path = tmp_path / "app.py"
+    source_path.write_bytes(b"safe")
+    manifest = source_upload.select_source(tmp_path)
+
+    # 1. Size/content modified
+    source_path.write_bytes(b"longer content modified")
+    with pytest.raises(http.CloudError, match="changed while the source archive was being built"):
+        source_upload._write_archive(tmp_path / "source1.zip", manifest.files)
+
+    # 2. Same size but mtime modified
+    source_path.write_bytes(b"evil")
+    selected = manifest.files[0]
+    os.utime(
+        source_path,
+        ns=(selected.mtime_ns + 1_000_000, selected.mtime_ns + 1_000_000),
+    )
+    with pytest.raises(http.CloudError, match="changed while the source archive was being built"):
+        source_upload._write_archive(tmp_path / "source2.zip", manifest.files)
+
+
+@pytest.mark.skipif(os.name != "nt", reason="Windows-specific filesystem settling test")
+def test_source_archive_windows_batch_creation_settling(tmp_path: Path) -> None:
+    for idx in range(50):
+        (tmp_path / f"file_{idx}.py").write_text(f"content = {idx}\n", encoding="utf-8")
+
+    manifest = source_upload.select_source(tmp_path)
+    archive_path = tmp_path / "batch_source.zip"
+    source_upload._write_archive(archive_path, manifest.files)
+    assert archive_path.is_file()
+
+
 def test_source_dry_run_never_calls_the_api(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch, capsys: Any
 ) -> None: