diff --git a/scripts/codex_package/README.md b/scripts/codex_package/README.md
index 6eb45eef47..7c89df6198 100644
--- a/scripts/codex_package/README.md
+++ b/scripts/codex_package/README.md
@@ -22,6 +22,10 @@ The builder creates a canonical Codex package directory:
 The package directory is the primary artifact. Archive formats such as
 `.tar.gz`, `.tar.zst`, and `.zip` are serializations of that directory.
 
+If `--target` is omitted, the builder uses the current host platform. If
+`--package-dir` is omitted, the builder creates a new temporary directory and
+prints its path after the package is built.
+
 ## Source-built artifacts
 
 Artifacts built from this repository are always built by the package builder in
diff --git a/scripts/codex_package/cli.py b/scripts/codex_package/cli.py
index c80f50a1a0..126f50e8cc 100644
--- a/scripts/codex_package/cli.py
+++ b/scripts/codex_package/cli.py
@@ -1,6 +1,7 @@
 """Command-line interface for building Codex package directories."""
 
 import argparse
+import tempfile
 from pathlib import Path
 
 from .archive import write_archive
@@ -11,6 +12,7 @@ from .layout import validate_package_dir
 from .ripgrep import resolve_rg_bin
 from .targets import TARGET_SPECS
 from .targets import PackageInputs
+from .targets import default_target
 
 
 def parse_args() -> argparse.Namespace:
@@ -20,9 +22,9 @@ def parse_args() -> argparse.Namespace:
     )
     parser.add_argument(
         "--target",
-        required=True,
+        default=argparse.SUPPRESS,
         choices=sorted(TARGET_SPECS),
-        help="Rust target triple for the package.",
+        help="Rust target triple for the package. Defaults to the host platform.",
     )
     parser.add_argument(
         "--version",
@@ -37,8 +39,11 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument(
         "--package-dir",
         type=Path,
-        required=True,
-        help="Output directory to create as the package root.",
+        default=argparse.SUPPRESS,
+        help=(
+            "Output directory to create as the package root. Defaults to a new "
+            "temporary directory."
+        ),
     )
     parser.add_argument(
         "--archive-output",
@@ -79,8 +84,13 @@ def parse_args() -> argparse.Namespace:
 
 def main() -> int:
     args = parse_args()
-    spec = TARGET_SPECS[args.target]
-    package_dir = args.package_dir.resolve()
+    spec = TARGET_SPECS[getattr(args, "target", None) or default_target()]
+    package_dir_arg = getattr(args, "package_dir", None)
+    package_dir = (
+        package_dir_arg.resolve()
+        if package_dir_arg is not None
+        else Path(tempfile.mkdtemp(prefix="codex-package-")).resolve()
+    )
 
     source_outputs = build_source_binaries(
         spec,
diff --git a/scripts/codex_package/targets.py b/scripts/codex_package/targets.py
index 0cb964a4cc..d3d3470e06 100644
--- a/scripts/codex_package/targets.py
+++ b/scripts/codex_package/targets.py
@@ -1,5 +1,6 @@
 """Supported package targets and default binary discovery."""
 
+import platform
 import stat
 from dataclasses import dataclass
 from pathlib import Path
@@ -78,6 +79,29 @@ TARGET_SPECS: dict[str, TargetSpec] = {
 }
 
 
+HOST_TARGETS: dict[tuple[str, str], str] = {
+    ("darwin", "aarch64"): "aarch64-apple-darwin",
+    ("darwin", "x86_64"): "x86_64-apple-darwin",
+    ("linux", "aarch64"): "aarch64-unknown-linux-musl",
+    ("linux", "x86_64"): "x86_64-unknown-linux-musl",
+    ("windows", "aarch64"): "aarch64-pc-windows-msvc",
+    ("windows", "x86_64"): "x86_64-pc-windows-msvc",
+}
+
+
+def default_target() -> str:
+    system = platform.system().lower()
+    machine = normalize_machine(platform.machine())
+    target = HOST_TARGETS.get((system, machine))
+    if target is None:
+        supported = ", ".join(sorted(TARGET_SPECS))
+        raise RuntimeError(
+            f"Unsupported host platform {platform.system()}/{platform.machine()}. "
+            f"Pass --target explicitly. Supported targets: {supported}"
+        )
+    return target
+
+
 def resolve_input_path(
     explicit_path: Path | None,
     description: str,
@@ -96,3 +120,12 @@ def resolve_input_path(
 
 def is_executable(path: Path) -> bool:
     return bool(path.stat().st_mode & (stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH))
+
+
+def normalize_machine(machine: str) -> str:
+    machine = machine.lower()
+    if machine in ("amd64", "x86_64"):
+        return "x86_64"
+    if machine in ("aarch64", "arm64"):
+        return "aarch64"
+    return machine