[mutable-arrays] enable vjp3 by default

PiperOrigin-RevId: 823700528

Author: mattjj

jax/_src/config.py

@@ -1836,7 +1836,7 @@ def _validate_default_device(val):
 
 vjp3 = bool_state(
     name='jax_vjp3',
-    default=False,
+    default=True,
     upgrade=True,
     help='Use new backward-pass code in jax.vjp')