diff --git a/scripts/run_tests.sh b/scripts/run_tests.sh
index a54b7163d3f6..7db931f521d3 100755
--- a/scripts/run_tests.sh
+++ b/scripts/run_tests.sh
@@ -71,6 +71,15 @@ echo "  (TZ=UTC LANG=C.UTF-8 PYTHONHASHSEED=0; clean env)"
 
 cd "$REPO_ROOT"
 
+# ── Pre-compile .pyc bytecode cache ─────────────────────────────────────────
+# Each test file runs in its own subprocess via run_tests_parallel.py.
+# Pre-building the bytecode cache once here (instead of each subprocess
+# compiling on first import) avoids redundant work across ~2000 processes.
+# Uses git to list tracked .py files (skips venv, node_modules, etc).
+echo "▶ pre-compiling bytecode cache"
+"$PYTHON" -m compileall -q -j 0 -- $(git ls-files '*.py') >/dev/null 2>&1 || true
+
+echo "▶ launching test runner"
 exec env -i \
   PATH="$PATH" \
   HOME="$HOME" \
@@ -78,7 +87,6 @@ exec env -i \
   LANG=C.UTF-8 \
   LC_ALL=C.UTF-8 \
   PYTHONHASHSEED=0 \
-  PYTHONDONTWRITEBYTECODE=1 \
   ${HERMES_RUN_SLOW_PET_TESTS:+HERMES_RUN_SLOW_PET_TESTS="$HERMES_RUN_SLOW_PET_TESTS"} \
   ${EXTRA_PYTHONPATH:+PYTHONPATH="$EXTRA_PYTHONPATH"} \
   ${EXTRA_PYTEST_PLUGINS:+PYTEST_PLUGINS="$EXTRA_PYTEST_PLUGINS"} \
diff --git a/scripts/run_tests_parallel.py b/scripts/run_tests_parallel.py
index b9cf5a97e15b..602e033f3d6d 100755
--- a/scripts/run_tests_parallel.py
+++ b/scripts/run_tests_parallel.py
@@ -260,8 +260,7 @@ def _run_one_file(
         stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT,
         text=True,
-        # skipping writing bytecode because we're running a bunch of parallel python processes on the same code
-        env={**os.environ, 'PYTHONDONTWRITEBYTECODE': '1'},
+        env=os.environ,
         # POSIX: place the child at the head of its own process group so
         # _kill_tree can SIGKILL the group atomically.
         # Windows: this maps to CREATE_NEW_PROCESS_GROUP in CPython 3.12+;