During June 2026, this developer contributed to the python/mypy repository by implementing closed TypedDicts in accordance with PEP 728, introducing strict key checking to enforce that only predefined keys are allowed in TypedDicts. Using Python and leveraging static analysis and type checking expertise, the work addressed multiple longstanding issues related to TypedDict misuse and improved the reliability of type definitions. This enhancement strengthened type safety by enabling earlier detection of errors involving extra dictionary keys, aligning mypy more closely with evolving Python typing standards. The contribution laid the groundwork for future TypedDict improvements and increased confidence in strict type validation for users.