# Kotlin Compatibility

The Kotlin compiler plugin API is not a stable API, so not every version of Metro will work with every version of the Kotlin compiler.

Starting with Metro `0.6.9`, Metro tries to support forward compatibility on a best-effort basis. Usually, it's `N+.2` (so a Metro version built against Kotlin `2.3.0` will try to support up to `2.3.20`.

| Kotlin version  | Metro versions (inclusive) | Notes                                |
|-----------------|----------------------------|--------------------------------------|
| 2.3.20-dev-5437 | 0.8.1 -                    |                                      |
| 2.3.0-RC        | 0.6.9, 0.6.11 -            | Reporting doesn't work until `0.7.3` |
| 2.3.0-Beta2     | 0.6.9, 0.6.11 -            | Reporting doesn't work until `0.7.3` |
| 2.3.0-Beta1     | 0.6.9, 0.6.11 -            |                                      |
| 2.2.21          | 0.6.6 -                    |                                      |
| 2.2.20          | 0.6.6 -                    |                                      |
| 2.2.10          | 0.4.0 - 0.6.5              |                                      |
| 2.2.0           | 0.4.0 - 0.6.5              |                                      |
| 2.1.21          | 0.3.1 - 0.3.8              |                                      |
| 2.1.20          | 0.1.2 - 0.3.0              |                                      |

Some releases may introduce prohibitively difficult breaking changes that require companion release, so check Metro's open PRs for one targeting that Kotlin version for details. There is a tested versions table at the bottom of this page that is updated with each Metro release.

## Tested Versions

[![CI](https://github.com/ZacSweers/metro/actions/workflows/ci.yml/badge.svg)](https://github.com/ZacSweers/metro/actions/workflows/ci.yml)

The following Kotlin versions are tested via CI:

| Kotlin Version  |
|-----------------|
| 2.3.20-dev-5437 |
| 2.3.0-RC3       |
| 2.3.0-RC2       |
| 2.3.0-RC        |
| 2.3.0-Beta2     |
| 2.3.0-Beta1     |
| 2.2.21          |
| 2.2.20          |

!!! note
    Versions without dedicated compiler-compat modules will use the nearest available implementation _below_ that version. See [`compiler-compat/version-aliases.txt`](https://github.com/ZacSweers/metro/blob/main/compiler-compat/version-aliases.txt) for the full list.

## What about Metro's stability?

See the [stability docs](stability.md).