# What changed in trio

> 10 changes in trio 0.33 to 0.34 from its official release notes, upgrade guides and advisories: 1 breaking, 2 deprecations, 1 new APIs and options. Each one cited. Sources checked 2026-10-21. HTML: https://unstale.sh/pypi/trio/

To see which of these apply to a repository, run `npx @unstale/cli init` in it.

## trio 0.34

### Breaking changes

- Using absolute deadlines on a cancel scope constructed with a relative deadline now raises; replace the CancelScope object to switch it from relative to absolute. (0.34.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.34.0)

### New APIs and options

- Adds a field reporting the largest number of items ever held in the channel buffer, helping developers choose a sensible max_buffer_size based on real runs. (0.34.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.34.0)

### Behavior and default changes

- Adds support for Python 3.15 beta 4; this support may break in the future as things change. (0.34.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.34.0)

### Fixes and other changes

- Preserves the __cause__ and __context__ of exceptions raised before task_status.started() is called. (0.34.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.34.0)
- Corrects the error message for the stdout pipe check, which incorrectly said stdin. (0.34.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.34.0)
- Fixes behavior on Python 3.14+ to avoid the deprecated pathlib.PurePath.as_uri() path. (0.34.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.34.0)
- Fixes workers leaking the spawner's Context on py314t+ free-threaded builds. (0.34.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.34.0)

## trio 0.33

### Deprecations

- Deprecated in favor of pytest.RaisesExc. (0.33.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.33.0)
- Deprecated in favor of pytest.RaisesGroup. (0.33.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.33.0)

### Behavior and default changes

- Trio now supports Android's new sys.platform value. (0.33.0) — [release notes](https://github.com/python-trio/trio/releases/tag/v0.33.0)