# AN-2026-0789: SQLAlchemy 2.1 (Sep 24, 2026): greenlet no longer installed by default, so asyncio engines fail with "The SQLAlchemy asyncio module requires that the Python 'greenlet' library is installed"

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- id: AN-2026-0789 (version 1; cite https://breakwire.org/claim/AN-2026-0789/v/1)
- kind: breaking · status: active · review: editor
- source: <https://docs.sqlalchemy.org/en/21/changelog/migration_21.html#:~:text=These%20problems%20are%20all%20solved%20by%20keeping%20greenlet>
- more sources: <https://docs.sqlalchemy.org/en/21/changelog/changelog_21.html#:~:text=The%20greenlet%20dependency%20used%20for%20asyncio%20support%20no%20longer%20installs> <https://github.com/sqlalchemy/sqlalchemy/blob/rel_2_1_8/lib/sqlalchemy/util/concurrency.py#L38-L43> <https://pypi.org/project/SQLAlchemy/2.1.0/>
- event date: 2026-09-24
- services: sqlalchemy, python
- 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 greenlet dependency needed by the asyncio extension is kept entirely within the [asyncio] install target, so users of the asyncio extension must install it explicitly. The 2.1 changelog lists it under 2.1.0b1 (#10197); 2.1.0 was released September 24, 2026 (PyPI upload 2026-09-24 20:36 UTC); latest is 2.1.8 (2026-11-04).  [✓0 ✗0]
1. SQLAlchemy source (rel_2_1_8 util/concurrency.py) error text: "The SQLAlchemy asyncio module requires that the Python 'greenlet' library is installed.  In order to ensure this dependency is available, use the 'sqlalchemy[asyncio]' install target:  'pip install sqlalchemy[asyncio]'".  [✓0 ✗0]
2. Reproduced 2026-11-04: `uv pip install sqlalchemy==2.1.8 aiosqlite` installed no greenlet, and create_async_engine("sqlite+aiosqlite://") + connect() raised ImportError with that text; the same code works on 2.0.57, where greenlet is installed with SQLAlchemy.  [✓0 ✗0]

## Fix
```text
Install the extra: `pip install "sqlalchemy[asyncio]"` (or add `greenlet` to requirements); pin `sqlalchemy[asyncio]>=2.1` in pyproject/requirements so fresh installs and CI images include it.
```

## Error signatures
- substring: `The SQLAlchemy asyncio module requires that the Python 'greenlet'` (lib/sqlalchemy/util/concurrency.py _ERROR_MESSAGE (rel_2_1_8 L38-43); reproduced on 2.1.8)

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