Case study of migrating a large scale application (200k+ weekly users) to using Apollo Client 3.0 for data layer and state management. Features covered include - New BE GraphQL API to replace multiple separate api calls - Local resolver for REST API without GraphQL endpoint - Type policies using custom keyFields and cache references - Local state management with reactive variables for cache - Cache updates with queries and cache.modify The end result turned out great, but the talk will also cover potential pitfalls and how those were able to be overcome.