doc: update V8 ABI release policy

doc/contributing/maintaining/maintaining-V8.md

@@ -308,6 +308,10 @@ Revision_ from the 5.4 branch that can be useful in the update process above.
 We upgrade the version of V8 in Node.js `main` whenever a V8 release goes stable
 upstream, that is, whenever a new release of Chrome comes out.
 
+V8 updates can require a `NODE_MODULE_VERSION` bump if they change the native
+addon ABI. See the release process documentation for when
+`NODE_MODULE_VERSION` may be updated during a release line.
+
 Upgrading major versions would be much harder to do with the patch mechanism
 above. A better strategy is to
 

doc/contributing/releases.md

@@ -1379,10 +1379,25 @@ in the registry. Also include a change to the registry in your commit to
 reflect the newly used value. Ensure that the release commit removes the
 `-pre` suffix for the major version being prepared.
 
-It is current TSC policy to bump major version when ABI changes. If you
-see a need to bump `NODE_MODULE_VERSION` outside of a major release then
-you should consult the TSC. Commits may need to be reverted or a major
-version bump may need to happen.
+Starting with Node.js 27, changes that break the native addon ABI and require
+a `NODE_MODULE_VERSION` bump, such as V8 updates, may land during the Alpha and
+Current phases of a release line. Such changes should still be labeled as
+semver-major on the default branch. When they are promoted to the release line,
+they may land in semver-minor releases as long as the ABI change is clearly
+documented in the release notes. If the change also removes or modifies APIs
+that addons use, so that addons need source changes rather than only a
+rebuild, the release notes should say so.
+
+Once a release line enters LTS, ABI-breaking changes are strongly discouraged.
+They should only land when they are necessary, such as for security fixes, and
+when there is no way to make the change without breaking the ABI. Changes that
+are not necessary for an LTS line, such as adding fields to a struct to expose
+more information in a diagnostic API, do not meet this bar. In practice, this
+means V8 is not updated on a release line after it enters LTS.
+
+This policy applies to addons that depend on V8, Node.js, or other non-Node-API
+native interfaces. Node-API remains the recommended interface for native addons
+that require ABI stability across Node.js versions.
 
 ### Test releases and release candidates