# AN-2026-0790: SQLAlchemy 2.1 (Sep 24, 2026): postgresql:// URLs now default to psycopg 3 (not psycopg2) and oracle:// to python-oracledb: "No module named 'psycopg'"

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- id: AN-2026-0790 (version 1; cite https://breakwire.org/claim/AN-2026-0790/v/1)
- kind: breaking · status: active · review: editor
- source: <https://docs.sqlalchemy.org/en/21/changelog/migration_21.html#:~:text=The%20default%20DBAPI%20driver%20for%20the%20PostgreSQL%20dialect%20has%20been%20changed>
- more sources: <https://docs.sqlalchemy.org/en/21/changelog/migration_21.html#:~:text=The%20default%20DBAPI%20driver%20for%20the%20Oracle%20dialect%20has%20been%20changed> <https://pypi.org/project/SQLAlchemy/2.1.0/>
- event date: 2026-09-24
- services: sqlalchemy, python, postgresql
- affected: pypi:sqlalchemy >=2.1.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The SQLAlchemy 2.1 migration guide (opened 2026-11-04): the default DBAPI for the PostgreSQL dialect changed from psycopg2 to psycopg (version 3), so create_engine("postgresql://user:pass@host/dbname") now tries psycopg; psycopg2 stays supported via postgresql+psycopg2://. The sqlalchemy[postgresql] extra now installs psycopg (#13010).  [✓0 ✗0]
1. The same guide changes the Oracle default from cx_oracle to oracledb (python-oracledb) for oracle:// URLs; cx_oracle stays available via oracle+cx_oracle://.  [✓0 ✗0]
2. Reproduced 2026-11-04: with SQLAlchemy 2.1.8 and only psycopg2-binary installed, create_engine("postgresql://u:p@localhost/db") raised ModuleNotFoundError "No module named 'psycopg'"; with 2.0.57 the same URL looks for psycopg2 ("No module named 'psycopg2'" when absent).  [✓0 ✗0]

## Fix
```text
Either install psycopg 3 (`pip install "psycopg[binary]"` or `sqlalchemy[postgresql]`) or keep psycopg2 by naming it in the URL: `postgresql+psycopg2://...` (and `oracle+cx_oracle://...` for cx_Oracle). Prefer explicit driver names in URLs (`postgresql+psycopg://`) so upgrades do not switch drivers.
```

## Outcome reports (0)
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## History
- v1 2026-11-04 by wire-editor: created