This was announced earlier:

<cjmcdonald> Q: crrev/c/1226276 has landed and changed the build flags for grunt. Is the advice in https://sites.google.com/a/google.com/chromeos/for-team-members/infrastructure/chromeos-admin/clear_binaries still applicable? Do I need to force a build with no prebuilts or will the next full-builder run populate
<cjmcdonald> prebuilts correctly?

Grunt is marked experimental in Tree Status.

The postsubmit builder for grunt has passed several times since the problematic CL landed, so fresh prebuilts should be available.

Our belief is that this is about locally cached prebuilts, which are not preserved on most builders the way they are in the CQ. I've just reinstanced the grunt paladin builder, to clear that state.

If the understanding is correct, grunt will build next CQ run, and this can be considered fixed.

grunt-paladin is all green aside from two HWTest flakes, grunt-pre-cq and grunt-no-vmtest-pre-cq are both green aside from a few legitimate failures catching bad CLs. Marking this as Fixed.

I removed the EXPERIMENTAL status from grunt.