diff --git a/pyproject.toml b/pyproject.toml
index 3e131ff698..48effe0fa2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -290,6 +290,12 @@ tests_dir = [
 also_copy = [
     "litellm/",
 ]
+# Run the test suite once before mutation to gather line coverage, then skip
+# mutating lines no test exercises. Those mutants would survive regardless
+# (no test hits the line to kill them), so generating them wastes hours of CI.
+# The score now reads as "mutation score over covered code" — pair with a
+# line-coverage number when reporting.
+mutate_only_covered_lines = true
 # Disable rerun/parallel plugins for mutation runs:
 # - pytest-retry triggers an `INTERNALERROR: no option named 'filtered_exceptions'`
 #   when invoked via mutmut's in-process `pytest.main()` call.