Python Enhancement Proposals have introduced a new standard for structured startup configuration in Python. PEP 829 proposes a TOML-based configuration file format to replace the .pth file mechanism used by site.py during interpreter startup. The new format provides structured configuration for extending sys.path and executing package initialization code. This design addresses several problems with the current .pth file mechanism, including the conflation of path configuration with arbitrary code execution. The new format uses files named .site.toml, which supersede parallel .pth files, allowing for an easy migration path and continued support for older Pythons in parallel. Package authors can migrate to a .site.toml file, and tool makers should generate .site.toml files alongside or instead of .pth files. The TOML format is easy to generate programmatically using tomllib or string formatting. Build backends should ensure that the prefix matches the package name. Installers may validate or enforce that the prefix matches the package name. A reference implementation is provided as modifications to Lib/site.py. Tests are provided in Lib/test/test_site.py. This PEP improves the security posture of interpreter startup by providing a more structured, auditable, and amenable mechanism for future policy controls. Package authors and tool makers should review the new format and migrate to .site.toml files to take advantage of the improved configuration capabilities.