diff --git a/components/l4d2-host-lib/src/l4d2host/steam_install.py b/components/l4d2-host-lib/src/l4d2host/steam_install.py
new file mode 100644
index 0000000..5282dbc
--- /dev/null
+++ b/components/l4d2-host-lib/src/l4d2host/steam_install.py
@@ -0,0 +1,37 @@
+from pathlib import Path
+from typing import Callable
+
+from l4d2host.process import run_command
+
+
+class SteamInstaller:
+    def __init__(self, install_dir: Path = Path("/opt/l4d2/installation"), steamcmd: str = "steamcmd"):
+        self.install_dir = install_dir
+        self.steamcmd = steamcmd
+
+    def install_or_update(
+        self,
+        *,
+        on_stdout: Callable[[str], None] | None = None,
+        on_stderr: Callable[[str], None] | None = None,
+        passthrough: bool = False,
+    ) -> None:
+        for platform in ("windows", "linux"):
+            run_command(
+                [
+                    self.steamcmd,
+                    "+force_install_dir",
+                    str(self.install_dir),
+                    "+login",
+                    "anonymous",
+                    "+@sSteamCmdForcePlatformType",
+                    platform,
+                    "+app_update",
+                    "222860",
+                    "validate",
+                    "+quit",
+                ],
+                on_stdout=on_stdout,
+                on_stderr=on_stderr,
+                passthrough=passthrough,
+            )
diff --git a/components/l4d2-host-lib/tests/test_install.py b/components/l4d2-host-lib/tests/test_install.py
new file mode 100644
index 0000000..5ef73c8
--- /dev/null
+++ b/components/l4d2-host-lib/tests/test_install.py
@@ -0,0 +1,35 @@
+import subprocess
+
+import pytest
+
+from l4d2host.steam_install import SteamInstaller
+
+
+def test_windows_then_linux(monkeypatch: pytest.MonkeyPatch) -> None:
+    calls: list[list[str]] = []
+
+    def fake_run_command(cmd, **kwargs):
+        del kwargs
+        calls.append(list(cmd))
+
+    monkeypatch.setattr("l4d2host.steam_install.run_command", fake_run_command)
+    SteamInstaller().install_or_update()
+    assert "windows" in calls[0]
+    assert "linux" in calls[1]
+
+
+def test_fail_fast_on_first_failure(monkeypatch: pytest.MonkeyPatch) -> None:
+    calls: list[list[str]] = []
+
+    def fake_run_command(cmd, **kwargs):
+        del kwargs
+        calls.append(list(cmd))
+        if len(calls) == 1:
+            raise subprocess.CalledProcessError(returncode=1, cmd=cmd)
+
+    monkeypatch.setattr("l4d2host.steam_install.run_command", fake_run_command)
+
+    with pytest.raises(subprocess.CalledProcessError):
+        SteamInstaller().install_or_update()
+
+    assert len(calls) == 1