diff --git a/CHANGELOG.md b/CHANGELOG.md
index 28a09a9..55b3ec5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,17 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
 
+### Fixed
+
+- **`__version__` reported `0.1.0` for the whole of `0.1.1`.** The release
+  bumped the literal in `pyproject.toml` and left the second one in
+  `claude_batch_runner/__init__.py` behind, so anything reading the package
+  attribute saw the previous release. `__version__` is now *derived* from
+  installed metadata, leaving `pyproject.toml` as the single source of truth
+  (which is what `release.yml` already cross-checks against the git tag), and
+  `tests/test_version.py` fails if the two ever disagree again. A source
+  checkout that was never pip-installed reports `0.0.0.dev0`.
+
 ### Added
 
 - **`cwd` and `permission_mode` on `call_agent`** — two optional keyword-only
diff --git a/claude_batch_runner/__init__.py b/claude_batch_runner/__init__.py
index b686ff3..925c41d 100644
--- a/claude_batch_runner/__init__.py
+++ b/claude_batch_runner/__init__.py
@@ -10,6 +10,9 @@
 Public API is re-exported here.
 """
 
+from importlib.metadata import PackageNotFoundError
+from importlib.metadata import version as _installed_version
+
 from claude_batch_runner.driver import (
     DEFAULT_AGENT_TIMEOUT_S,
     AgentError,
@@ -52,4 +55,10 @@
     "verify_unit",
 ]
 
-__version__ = "0.1.0"
+# Derived, never written by hand. `pyproject.toml` is the single source of
+# truth — release.yml already cross-checks it against the git tag — and a
+# second literal here drifted the moment 0.1.1 bumped one and not the other.
+try:
+    __version__ = _installed_version("claude-batch-runner")
+except PackageNotFoundError:  # source checkout, never pip-installed
+    __version__ = "0.0.0.dev0"
diff --git a/tests/test_version.py b/tests/test_version.py
new file mode 100644
index 0000000..1cc9911
--- /dev/null
+++ b/tests/test_version.py
@@ -0,0 +1,35 @@
+"""`__version__` agrees with pyproject.toml. Never spawns a real `claude` process."""
+
+from __future__ import annotations
+
+import tomllib
+from pathlib import Path
+
+import pytest
+
+import claude_batch_runner
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+PYPROJECT = REPO_ROOT / "pyproject.toml"
+
+
+def _declared_version() -> str:
+    with PYPROJECT.open("rb") as fh:
+        return tomllib.load(fh)["project"]["version"]
+
+
+def test_version_matches_pyproject():
+    """0.1.1 bumped pyproject and left `__version__` at 0.1.0 for a whole release.
+
+    `__version__` is now derived from installed metadata rather than a second
+    literal, so the only way this can disagree is a stale editable install --
+    which is itself worth failing on, because every other check in the repo
+    (release.yml's tag cross-check included) trusts pyproject.
+    """
+    assert claude_batch_runner.__version__ == _declared_version()
+
+
+def test_version_is_not_the_uninstalled_fallback():
+    """The PackageNotFoundError branch must not be what the suite exercises."""
+    if claude_batch_runner.__version__ == "0.0.0.dev0":
+        pytest.fail("package is not installed; run `pip install -e .[dev]` before pytest")