DOC: clarify API compatibility discussion & mention EffVer

docs/api_compatibility.md

@@ -8,8 +8,15 @@ JAX is constantly evolving, and we want to be able to make improvements to its
 APIs. That said, we want to minimize churn for the JAX user community, and we
 try to make breaking changes rarely.
 
-JAX follows a 3 month deprecation policy. When an incompatible change is made
+## JAX Versioning
-to an API, we will make our best effort to obey the following procedure:
+JAX uses [Effort-based versioning](https://jacobtomlinson.dev/effver/) (see
+{ref}`jep-effver`), and is currently in the Zero version phase.
+This means that for version `0.X.Y`, incrementing `Y` will introduce minor
+breaking changes, and incrementing `X` will introduce major breaking changes.
+
+For any breaking change, JAX currently follows a 3 month deprecation policy.
+When an incompatible change is made to an API, we will make our best effort
+to obey the following procedure:
 * the change will be announced in `CHANGELOG.md` and in the doc string for the
   deprecated API, and the old API will issue a `DeprecationWarning`.
 * three months after the `jax` release that deprecated an API, we may remove the
@@ -47,16 +54,44 @@ prefixed with underscores, although we do not entirely comply with this yet.
 
 ## What is not covered?
 
-*  anything prefixed with an underscore.
+### Explicitly private APIs
-* `jax._src`
+Any API or import path prefixed with an underscore is explicitly private,
-* `jax.core`
+and may change without warning between JAX releases. We are working to move
-* `jax.lib`
+all private APIs into `jax._src` to make these expectations more clear.
-* `jax.interpreters`
+
+### Legacy internal APIs
+In addition, there are several legacy modules that currently expose some
+private APIs without an underscore, including:
+
+- `jax.core`
+- `jax.interpreters`
+- `jax.lib`
+- `jax.util`
+
+We are actively working on deprecating these modules and the APIs they contain.
+In most cases, such deprecations will follow the 3 month deprecation period,
+but this may not always be possible. If you use any such APIs, please expect
+them to be deprecated soon, and seek alternatives.
+
+### Experimental and example libraries
+The following modules include code for experimental or demonstration purposes,
+and API may change between releases without warning:
+
 * `jax.experimental`
 * `jax.example_libraries`
-* `jax.extend` (see [details](https://jax.readthedocs.io/en/latest/jax.extend.html))
 
-This list is not exhaustive.
+We understand that some users depend on `jax.experimental`, and so in most cases
+we follow the 3 month deprecation period for changes, but this may not always be
+possible.
+
+### JAX extend
+The {mod}`jax.extend` module includes semi-public JAX internal APIs that are
+meant for use by downstream projects, but do not have the same stability
+guarantees of the main JAX package. If you have code that uses `jax.extend`,
+we would strongly recommend CI tests against JAX's nightly releases, so as to
+catch potential changes before they are released.
+
+For details on `jax.extend`, see the [`jax.extend` module docuementation](https://jax.readthedocs.io/en/latest/jax.extend.html), or the design document, {ref}`jax-extend-jep`.
 
 ## Numerics and randomness
 

docs/jep/25516-effver.md

@@ -1,3 +1,4 @@
+(jep-effver)=
 # JEP 25516: Effort-based versioning for JAX
 
 This document proposes that the JAX core library should explicitly adopt