diff --git a/scripts/test-parallel.mjs b/scripts/test-parallel.mjs
index a4a9c3bd38..ccfaa11108 100644
--- a/scripts/test-parallel.mjs
+++ b/scripts/test-parallel.mjs
@@ -123,8 +123,9 @@ const parallelRuns = keepGatewaySerial ? runs.filter((entry) => entry.name !== "
 const serialRuns = keepGatewaySerial ? runs.filter((entry) => entry.name === "gateway") : [];
 const localWorkers = Math.max(4, Math.min(16, os.cpus().length));
 const defaultUnitWorkers = localWorkers;
-const defaultExtensionsWorkers = Math.max(1, Math.min(4, Math.floor(localWorkers / 4)));
-const defaultGatewayWorkers = Math.max(1, Math.min(4, localWorkers));
+// Local perf: extensions tend to be the critical path under parallel vitest runs; give them more headroom.
+const defaultExtensionsWorkers = Math.max(1, Math.min(6, Math.floor(localWorkers / 2)));
+const defaultGatewayWorkers = Math.max(1, Math.min(2, Math.floor(localWorkers / 4)));
 
 // Keep worker counts predictable for local runs; trim macOS CI workers to avoid worker crashes/OOM.
 // In CI on linux/windows, prefer Vitest defaults to avoid cross-test interference from lower worker counts.