diff --git a/vitest.config.ts b/vitest.config.ts
index bd474d7b7..c2d9435ad 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -25,6 +25,16 @@ export default defineConfig({
     globals: true,
     environment: 'node',
     globalSetup: './vitest.setup.ts',
+    // Opt the suite out of telemetry. Many tests spawn the real CLI, which runs
+    // the preAction hook like any user invocation: it would persist an
+    // anonymousId into the developer's *real* global config and POST a
+    // command_executed event per spawn. Workers inherit this env, and so do the
+    // CLI child processes they spawn. Telemetry's own tests delete these vars
+    // before asserting, so they are unaffected.
+    env: {
+      OPENSPEC_TELEMETRY: '0',
+      DO_NOT_TRACK: '1',
+    },
     // Tests rely on per-file process isolation (e.g., `process.cwd()` assumptions).
     pool: 'forks',
     maxWorkers: resolveMaxWorkers(),