diff --git a/tests/unit/test_version_consistency.py b/tests/unit/test_version_consistency.py
new file mode 100644
index 0000000..06ccdae
--- /dev/null
+++ b/tests/unit/test_version_consistency.py
@@ -0,0 +1,33 @@
+"""The package version must be declared identically in both places.
+
+Releases bump the version in two files — ``pyproject.toml`` (what PyPI ships)
+and ``blockrun_llm/__init__.py`` (what ``blockrun_llm.__version__`` reports).
+These drifted once (1.4.6 bumped pyproject but not __init__, so installed
+copies under-reported as 1.4.5). This test fails CI if they ever diverge
+again, instead of the mismatch shipping silently to PyPI.
+
+Parsed with a regex rather than tomllib so it runs on Python 3.9 (no stdlib
+TOML parser before 3.11) without adding a tomli dependency.
+"""
+
+import re
+from pathlib import Path
+
+import blockrun_llm
+
+_PYPROJECT = Path(__file__).resolve().parents[2] / "pyproject.toml"
+
+
+def _pyproject_version() -> str:
+    text = _PYPROJECT.read_text(encoding="utf-8")
+    # First top-level `version = "..."` under [project] / [tool.poetry] etc.
+    match = re.search(r'(?m)^\s*version\s*=\s*"([^"]+)"', text)
+    assert match, "no version declared in pyproject.toml"
+    return match.group(1)
+
+
+def test_version_matches_pyproject():
+    assert blockrun_llm.__version__ == _pyproject_version(), (
+        f"version drift: __init__.py={blockrun_llm.__version__!r} "
+        f"!= pyproject.toml={_pyproject_version()!r} — bump BOTH on release"
+    )