anyio breaking changes

4.14.2

3 breaking changes, first published July 12, 2026.

• Behavior changed ByteReceiveStream.receive
  Calls passing a max_bytes that is not a positive integer now raise ValueError. Pass a positive integer for max_bytes. github.com
• Behavior changed CapacityLimiter.acquire_nowait
  On the trio backend, a failed non-blocking acquire now raises anyio.WouldBlock. Code that catches trio.WouldBlock must catch anyio.WouldBlock instead. github.com
• Behavior changed CapacityLimiter.acquire_nowait_on_behalf_of
  On the trio backend, a failed non-blocking acquire now raises anyio.WouldBlock. Code that catches trio.WouldBlock must catch anyio.WouldBlock instead. github.com

4.14.0

47 breaking changes, first published June 15, 2026.

• Behavior changed anyio.CancelScope
  Instances of these classes no longer accept arbitrary new attributes, so code or subclasses that set extra attributes on them will break. github.com
• Behavior changed anyio.CapacityLimiter
  Instances of these classes no longer accept arbitrary new attributes, so code or subclasses that set extra attributes on them will break. github.com
• Behavior changed anyio.Condition
  Instances of these classes no longer accept arbitrary new attributes, so code or subclasses that set extra attributes on them will break. github.com
• Behavior changed anyio.Event
  Instances of these classes no longer accept arbitrary new attributes, so code or subclasses that set extra attributes on them will break. github.com
• Behavior changed anyio.Lock
  Instances of these classes no longer accept arbitrary new attributes, so code or subclasses that set extra attributes on them will break. github.com
• Behavior changed anyio.ResourceGuard
  Instances of these classes no longer accept arbitrary new attributes, so code or subclasses that set extra attributes on them will break. github.com
• Behavior changed anyio.Semaphore
  Instances of these classes no longer accept arbitrary new attributes, so code or subclasses that set extra attributes on them will break. github.com
• Signature changed anyio.abc.AsyncBackend.run_async_from_thread
  Was @classmethod def run_async_from_thread(cls, func: Callable[[Unpack[PosArgsT]], Awaitable[T_Retval]], args: tuple[Unpack[PosArgsT]], token: object) -> T_Retval; now @classmethod def run_async_from_thread(cls, func... pypi.org
• Signature changed anyio.abc.TaskGroup.start
  The annotation now accepts only callables returning coroutine-like objects, not arbitrary awaitables. Type-checked code passing other awaitables will fail type checking. pypi.org
• Signature changed anyio.abc.TaskGroup.start_soon
  start_soon() returns a TaskHandle instead of its previous return value. Code that relies on the old return value must be updated. pypi.org

And 37 more in this version.

4.13.0

6 breaking changes, first published March 24, 2026.

• Removed
  Python 3.9 is no longer supported by this release; users on Python 3.9 must upgrade their interpreter or stay on an older anyio version. github.com
• Signature changed anyio.functools.AsyncLRUCacheWrapper.__init__
  Was def __init__(self, func: Callable[P, Awaitable[T]], maxsize: int | None, typed: bool, always_checkpoint: bool); now def __init__(self, func: Callable[P, Awaitable[T]], maxsize: int | None, typed: bool, always_checkpoint: bool, ttl: int... pypi.org
• Signature changed anyio.functools.lru_cache
  Was def lru_cache(func: Callable[P, Coroutine[Any, Any, T]] | Callable[..., T] | None = None, /, *, maxsize: int | None = 128, typed: bool = False, always_checkpoint: bool = False) -> AsyncLRUCacheWrapper[P, T] |... pypi.org
• Signature changed anyio.streams.file.FileReadStream.__init__
  Was def __init__(self, file: BinaryIO); now def __init__(self, file: IO[bytes]). pypi.org
• Signature changed anyio.streams.file.FileStreamAttribute.file
  Was file: BinaryIO; now file: IO[bytes]. pypi.org
• Signature changed anyio.streams.file.FileWriteStream.__init__
  Was def __init__(self, file: BinaryIO); now def __init__(self, file: IO[bytes]). pypi.org

4.12.1

4 breaking changes, first published January 6, 2026.

• Removed anyio.abc.AsyncBackend.create_blocking_portal
  AsyncBackend.create_blocking_portal was removed in anyio 4.12.1 pypi.org
• Removed anyio.abc.BlockingPortal.__new__
  BlockingPortal.__new__ was removed in anyio 4.12.1 pypi.org
• Behavior changed
  Functions that previously raised the private NoCurrentAsyncBackend exception now raise the public NoEventLoopError. Code that catches NoCurrentAsyncBackend must catch NoEventLoopError instead. github.com
• Signature changed anyio.functools.AsyncLRUCacheWrapper.__init__
  Was def __init__(self, func: Callable[..., Awaitable[T]], maxsize: int | None, typed: bool, always_checkpoint: bool); now def __init__(self, func: Callable[P, Awaitable[T]], maxsize: int | None, typed: bool, always_checkpoint: bool). pypi.org

4.12.0

125 breaking changes, first published November 28, 2025.

• Removed anyio.from_thread.CancelScope
  anyio.from_thread.CancelScope was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.create_task_group
  anyio.from_thread.create_task_group was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.Event
  anyio.from_thread.Event was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.EventLoopToken
  anyio.from_thread.EventLoopToken was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.get_async_backend
  anyio.from_thread.get_async_backend was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.get_cancelled_exc_class
  anyio.from_thread.get_cancelled_exc_class was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.NoEventLoopError
  anyio.from_thread.NoEventLoopError was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.PosArgsT
  anyio.from_thread.PosArgsT was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.run_eventloop
  anyio.from_thread.run_eventloop was removed in anyio 4.12.0 pypi.org
• Removed anyio.from_thread.T_co
  anyio.from_thread.T_co was removed in anyio 4.12.0 pypi.org

And 115 more in this version.

4.11.0

10 breaking changes, first published September 23, 2025.

• Renamed anyio.from_thread.AsyncBackend
  Use anyio.lowlevel.AsyncBackend instead. pypi.org
• Behavior changed
  After a TCP stream is closed, send() on asyncio now raises ClosedResourceError instead of BrokenResourceError, so code catching BrokenResourceError in this case must catch ClosedResourceError instead. github.com
• Default changed anyio.abc.TaskStatus
  Code relying on the previous Any default type argument may see different type checking results and should specify the type argument explicitly. github.com
• Configuration changed
  Users of Trio older than 0.31.0 must upgrade Trio to install or run this release. github.com
• Signature changed anyio.CancelScope.cancel
  Was def cancel(self) -> None; now def cancel(self, reason: str | None = None) -> None. pypi.org
• Signature changed anyio.from_thread.run
  Was def run(func: Callable[[Unpack[PosArgsT]], Awaitable[T_Retval]], *args: Unpack[PosArgsT]) -> T_Retval; now def run(func: Callable[[Unpack[PosArgsT]], Awaitable[T_Retval]], *args: Unpack[PosArgsT], token: EventLoopToken | None = None)... pypi.org
• Signature changed anyio.from_thread.run_sync
  Was def run_sync(func: Callable[[Unpack[PosArgsT]], T_Retval], *args: Unpack[PosArgsT]) -> T_Retval; now def run_sync(func: Callable[[Unpack[PosArgsT]], T_Retval], *args: Unpack[PosArgsT], token: EventLoopToken | None = None) -> T_Retval. pypi.org
• Signature changed anyio.lowlevel.current_token
  Was def current_token() -> object; now def current_token() -> EventLoopToken. pypi.org
• Signature changed anyio.pytest_plugin.pytest_configure
  Was def pytest_configure(config: Any) -> None; now def pytest_configure(config: pytest.Config) -> None. pypi.org
• Signature changed anyio.pytest_plugin.pytest_pycollect_makeitem
  Was def pytest_pycollect_makeitem(collector: Any, name: Any, obj: Any) -> None; now def pytest_pycollect_makeitem(collector: pytest.Module | pytest.Class, name: str, obj: object) -> None. pypi.org

Check your code

These are the changes. To see which of them reach your code, scan a public repository, or have your coding agent call check_code with your manifest or lockfile over MCP. The API reads every change in every version, not only the newest. On Team and up, a fix pull request opens for the changes that reach a connected repository. Nothing merges or deploys.