Upgrading from dbt below 1.8 to dbt-core 1.8+ failed during install, because 1.8 split the adapter code out into the separate dbt-adapters package. Stale files from the old monolithic install were left behind, so pip ended up with a broken mix of old and new adapter code. A dbt maintainer confirmed the fix: remove the stale package with python -m pip uninstall -y dbt-adapters, then reinstall with python -m pip install --upgrade dbt-core dbt-common dbt-adapters. Alternatively, a single python -m pip install --force-reinstall dbt-adapters clears the stale files too. The reporter tried the uninstall/reinstall and replied that it worked.