During September 2025, Celik focused on improving the correctness and reliability of immutable Thrift Python Sets in the facebook/fbthrift repository. He addressed a subtle bug in the implementation of rich comparison operators, ensuring that greater-than and greater-than-or-equal-to comparisons now align with Python’s set partial order semantics. To validate these changes, Celik developed comprehensive unit tests covering subset and superset behaviors, enhancing regression protection and test coverage for immutable collections. His work, primarily using Python and leveraging software development and unit testing expertise, targeted downstream bugs and contributed to more predictable and robust behavior for Thrift clients relying on set operations.