Here is the code that works based on the above

curl -X PUT \
                "${DATABRICKS_HOST}/api/2.0/serving-endpoints/databricks-claude-opus-4-1/ai-gateway" \
 -H "Authorization: Bearer ${DATABRICKS_TOKEN}" \
 -H "Content-Type: application/json" \
 -d '{
            "rate_limits": [
            {
                        "key":"user",
                        "renewal_period": "minute",
                "tokens": 99999
                },
            {
                        "key":"user",
                        "renewal_period": "minute",
                "calls": 9
                }
                ],
                "usage_tracking_config": { "enabled": true }
         }'
}

To get principal to work the call should look like this based on my experimentation:

curl -X PUT \
                "${DATABRICKS_HOST}/api/2.0/serving-endpoints/databricks-claude-opus-4-1/ai-gateway" \
 -H "Authorization: Bearer ${DATABRICKS_TOKEN}" \
 -H "Content-Type: application/json" \
 -d '{
            "rate_limits": [
            {
                        "key":"user",
                        "principal":"sfibich1@xyz.com",
                        "renewal_period": "minute",
                "tokens": 99999
                },
            {
                        "key":"user",
                        "renewal_period": "minute",
                "calls": 9
                }
                ],
                "usage_tracking_config": { "enabled": true }
         }'
}