What role did they have? Unless you mean the pivots that Twitter hired full time? I worked at Twitter during the entire transition from the monorail to the curr

What role did they have? Unless you mean the pivots that Twitter hired full time? I worked at Twitter during the entire transition from the monorail to the current architecture and there was ~0 Pivotal Labs involvement in that process. I know they had a big impact on the earlier phase of Twitter but when it comes to getting rid of the fail whale a large part of the credit goes to Marius and Raffi, neither one of whom were Pivots and I can't think of a single Pivot that built a service at Twitter that is in production today.