Developed a robust TTL state model for Cosmos DB within the Azure/azure-sdk-for-rust repository, focusing on backend development using Rust. The work introduced a TTLState enumeration to explicitly represent different expiration states, replacing the previous duration-based approach and aligning closely with Cosmos DB TTL semantics. By refactoring TTL deserialization logic, the changes eliminated edge-case panics and clarified TTL behavior across various configurations, reducing runtime errors and improving developer ergonomics. This feature enhanced safety and correctness in handling TTL configurations, ensuring that the SDK’s behavior matches Azure Cosmos DB documentation and enabling safer, more predictable defaults for developers working with Rust.