For large-scale mobile apps, software reliability is of critical importance. At the same time, developers need to be able to move fast in developing new features and products. In this talk, I will describe two recent projects on using pluggable type systems to reduce the tension between these seemingly-conflicting needs. First, I will present NullAway, a novel nullability type system for Java. NullAway improves on previous work by reducing build-time overhead and requiring fewer annotations through carefully-targeted unsoundness. Then, I will describe more recent work on the Object Construction Checker, a novel type system to ensure the safe usage of builders and other complex schemes for flexible object construction.