ERROR: Registering runner... failed runner=38BUk9-k status=404 Not Found

For people stumbling onto this issue from Google.

I was using gitlab-ci-multi-runner@1.10.0 with the latest EE GDK (10.0) and running into the same 404 error

ERROR: Registering runner... failed                 runner=xxx status=404 Not Found
PANIC: Failed to register this runner. Perhaps you are having network problems

After some pain, I figured out the compatibility chart no longer shows gitlab-ci-multi-runner@1.10.0 compatible with GitLab 10.0. My guess is the API endpoint moved from POST /ci/api/v1/builds/register.json which seems confirmed by

I had to update gitlab-ci-multi-runner@9.5.0,