diff --git a/scripts/codex_package/cli.py b/scripts/codex_package/cli.py
index fa569e9ae7..de081fe148 100644
--- a/scripts/codex_package/cli.py
+++ b/scripts/codex_package/cli.py
@@ -45,6 +45,10 @@ def parse_package_version(value: str) -> str:
 
 
 def parse_args() -> argparse.Namespace:
+    return create_parser().parse_args()
+
+
+def create_parser() -> argparse.ArgumentParser:
     parser = argparse.ArgumentParser(
         description="Build a canonical Codex package directory and optional archive.",
         formatter_class=argparse.ArgumentDefaultsHelpFormatter,
@@ -169,11 +173,18 @@ def parse_args() -> argparse.Namespace:
             "scripts/codex_package/rg."
         ),
     )
-    return parser.parse_args()
+    return parser
 
 
 def main() -> int:
     args = parse_args()
+    package_dir = assemble_package(args)
+    archive_package(package_dir, args)
+    return 0
+
+
+def assemble_package(args: argparse.Namespace) -> Path:
+    """Build the directory before optional downstream additions and archiving."""
     spec = TARGET_SPECS[getattr(args, "target", None) or default_target()]
     variant = PACKAGE_VARIANTS[args.variant]
     package_dir_arg = getattr(args, "package_dir", None)
@@ -228,14 +239,16 @@ def main() -> int:
     validate_package_dir(
         package_dir, variant, spec, include_zsh=inputs.zsh_bin is not None
     )
+    return package_dir
 
+
+def archive_package(package_dir: Path, args: argparse.Namespace) -> None:
     for archive_output in args.archive_output:
         archive_path = archive_output.resolve()
         write_archive(package_dir, archive_path, force=args.force)
         print(f"Built Codex package archive at {archive_path}")
 
     print(f"Built Codex package directory at {package_dir}")
-    return 0
 
 
 def resolve_optional_input_path(
diff --git a/scripts/codex_package/dotslash.py b/scripts/codex_package/dotslash.py
index 9252ae29f1..ba0adbe244 100644
--- a/scripts/codex_package/dotslash.py
+++ b/scripts/codex_package/dotslash.py
@@ -1,5 +1,6 @@
 """Fetch executable artifacts from checked-in DotSlash manifests."""
 
+import gzip
 import hashlib
 import json
 import shutil
@@ -184,6 +185,11 @@ def extract_archive_member(
     dest.parent.mkdir(parents=True, exist_ok=True)
     dest.unlink(missing_ok=True)
 
+    if artifact.archive_format == "gz":
+        with gzip.open(archive_path, "rb") as extracted, open(dest, "wb") as out:
+            shutil.copyfileobj(extracted, out)
+        return
+
     if artifact.archive_format == "tar.gz":
         with tarfile.open(archive_path, "r:gz") as archive:
             try:
@@ -218,5 +224,5 @@ def extract_archive_member(
 
     raise RuntimeError(
         f"Unsupported {artifact_label} archive format {artifact.archive_format!r}; "
-        "expected tar.gz or zip"
+        "expected gz, tar.gz or zip"
     )
diff --git a/scripts/codex_package/test_zsh.py b/scripts/codex_package/test_zsh.py
index 86d3c9fea8..20fa5dcd90 100644
--- a/scripts/codex_package/test_zsh.py
+++ b/scripts/codex_package/test_zsh.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 
+import gzip
 import hashlib
 import json
 from pathlib import Path
@@ -31,46 +32,51 @@ class ResolveZshBinTest(unittest.TestCase):
             fetch.assert_not_called()
 
     def test_uses_manifest_override(self) -> None:
-        with tempfile.TemporaryDirectory() as temp_dir:
-            root = Path(temp_dir)
-            archive = root / "codex-zsh.tar.gz"
-            source = root / "zsh"
-            source.write_bytes(b"standalone zsh")
-            with tarfile.open(archive, "w:gz") as tar:
-                tar.add(source, arcname="codex-zsh/bin/zsh")
+        for archive_format in ("tar.gz", "gz"):
+            with self.subTest(archive_format=archive_format):
+                with tempfile.TemporaryDirectory() as temp_dir:
+                    root = Path(temp_dir)
+                    archive = root / f"codex-zsh.{archive_format}"
+                    source = root / "zsh"
+                    source.write_bytes(b"standalone zsh")
+                    if archive_format == "gz":
+                        archive.write_bytes(gzip.compress(source.read_bytes()))
+                    else:
+                        with tarfile.open(archive, "w:gz") as tar:
+                            tar.add(source, arcname="codex-zsh/bin/zsh")
 
-            manifest = root / "codex-zsh"
-            manifest.write_text(
-                json.dumps(
-                    {
-                        "platforms": {
-                            "linux-x86_64": {
-                                "size": archive.stat().st_size,
-                                "hash": "sha256",
-                                "digest": hashlib.sha256(
-                                    archive.read_bytes()
-                                ).hexdigest(),
-                                "format": "tar.gz",
-                                "path": "codex-zsh/bin/zsh",
-                                "providers": [{"url": archive.as_uri()}],
+                    manifest = root / "codex-zsh"
+                    manifest.write_text(
+                        json.dumps(
+                            {
+                                "platforms": {
+                                    "linux-x86_64": {
+                                        "size": archive.stat().st_size,
+                                        "hash": "sha256",
+                                        "digest": hashlib.sha256(
+                                            archive.read_bytes()
+                                        ).hexdigest(),
+                                        "format": archive_format,
+                                        "path": "codex-zsh/bin/zsh",
+                                        "providers": [{"url": archive.as_uri()}],
+                                    }
+                                }
                             }
-                        }
-                    }
-                ),
-                encoding="utf-8",
-            )
+                        ),
+                        encoding="utf-8",
+                    )
 
-            with patch(
-                "codex_package.dotslash.default_cache_root",
-                return_value=root / "cache",
-            ):
-                zsh_bin = resolve_zsh_bin(
-                    TARGET_SPECS["x86_64-unknown-linux-musl"], manifest
-                )
+                    with patch(
+                        "codex_package.dotslash.default_cache_root",
+                        return_value=root / "cache",
+                    ):
+                        zsh_bin = resolve_zsh_bin(
+                            TARGET_SPECS["x86_64-unknown-linux-musl"], manifest
+                        )
 
-            self.assertIsNotNone(zsh_bin)
-            assert zsh_bin is not None
-            self.assertEqual(zsh_bin.read_bytes(), b"standalone zsh")
+                    self.assertIsNotNone(zsh_bin)
+                    assert zsh_bin is not None
+                    self.assertEqual(zsh_bin.read_bytes(), b"standalone zsh")
 
 
 if __name__ == "__main__":