# Toolchain policy Python 3.11 is the floor (`python = ">=3.11,<4.0"` in `pyproject.toml`), with CI on 3.11, 3.12, 3.13 and 3.14 on Linux, macOS and Windows. Raising the floor is a maintainer decision, recorded in the changelog, and moves with the rest of the camt053 suite in the same release. No distro-system Python is supported. Runtime dependencies carry upper bounds, except `certifi`, which is calendar-versioned and has to stay current. A dependency with a published advisory, direct or transitive, is floored in `pyproject.toml` so no affected version can resolve (for example `anyio>=4.14.2`, `starlette>=1.3.1`, `cryptography>=50.0.0`); `tests/test_advisory_floors.py` holds each floor. The CI and release tooling installs from hash-pinned `requirements/*.txt`, regenerated with `make pip-compile`.