Protobuf-java v4.33 restored gen code compatibility to 3.0.0. Upgrade
protobuf runtime and gen code to 4.33 should have minimum risks now.
See
[go/cloud-java:protobuf-4.x-upgrade](http://goto.google.com/cloud-java:protobuf-4.x-upgrade)
for details.

---------

Co-authored-by: cloud-java-bot <[email protected]>
Co-authored-by: Diego Marquez <[email protected]>

Add a new module java-showcase-3.25.8. This is a copy of the
java-showcase module with a different version (3.25.8) of protobuf gen
code. This is intended to test the compatibility between protobuf
runtime v4.33.0 and gen code 3.25.8.

Add [a new
step](https://github.com/googleapis/sdk-platform-java/blob/bccc9ded96f5313c22cd4543c25e49fb673792f6/.github/workflows/ci.yaml#L306-L312)
in CI to test this module.

Add a new module java-showcase-3.21.0. This is a copy of the
java-showcase module with a different version (3.21.0) of protobuf gen
code. This is intended to test the compatibility between protobuf
runtime v4.33.0 and gen code 3.21.0.

The [gen code contains makeExtensionsImmutable
method](https://github.com/googleapis/sdk-platform-java/blob/c80004ad3fdafbf43aa9adf4e8069ac3b4fefaa4/java-showcase-3.21.0/proto-gapic-showcase-v1beta1/src/main/java/com/google/showcase/v1beta1/AttemptSequenceRequest.java#L90)
which proves that it is generated with a protoc version prior to 3.21.7.


Add [a new
step](https://github.com/googleapis/sdk-platform-java/blob/c80004ad3fdafbf43aa9adf4e8069ac3b4fefaa4/.github/workflows/ci.yaml#L313-L319)
in CI to test this module.

…y tensorflow. (#4015)

Add protobuf 3.x compatibility tests with a third party library
tensorflow in showcase module.

Tensorflow depends on [protobuf-java
v3.21.9](https://github.com/tensorflow/java/blob/cbf942051d55291ba9bdb019b2f207f013889bba/tensorflow-core/pom.xml#L45)
gen code and runtime. This proves that client libraries with 4.33
runtime and gen code are compatible with a third party library that
contains 3.x gen code and runtime.

---------

Co-authored-by: cloud-java-bot <[email protected]>

Merge main to protobuf-4.x-rc. The main change from the main branch is
grpc-java 1.76.2 upgrade.

---------

Co-authored-by: Diego Marquez <[email protected]>
Co-authored-by: cloud-java-bot <[email protected]>
Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
Co-authored-by: Mend Renovate <[email protected]>

🤖 I have created a release *beep* *boop*
---


<details><summary>2.65.0-rc1</summary>

##
[2.65.0-rc1](v2.64.2...v2.65.0-rc1)
(2025-12-11)


### Features

* feat: Upgrade protobuf runtime and gen code to 4.33.
(#4000)
(ac25015)
* feat: configure rc releases to be on prerelease mode
(e9055b0)

### Bug Fixes

* fix: add rc versioning scheme
(2939320)


### Dependencies

* deps: update auth to 1.42.0-rc1 and http-client to 2.1.0-rc1
(#4014)
(0e01361)
* deps: Upgrade grpc to 1.76.2
(#4006)
* deps: update google api dependencies
(#3917)


---
This PR was generated with [Release
Please](https://github.com/googleapis/release-please). See
[documentation](https://github.com/googleapis/release-please#release-please).

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>