🎀 New default: beta=0.0 for GRPO

[qgallouedec]

What does this PR do?

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a GitHub issue? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[Copilot]

Pull Request Overview

This PR changes the GRPO KL coefficient default from 0.04 to 0.0 and updates related docs and tests.

• Sets beta default to 0.0 in code and docstrings
• Updates test to cover non-zero beta case (removes previous beta=0.0 test)
• Adds a documentation tip highlighting the new default and rationale

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
trl/trainer/grpo_config.py	Changed beta default from 0.04 to 0.0 and updated help text
tests/test_grpo_trainer.py	Renamed and updated test to use a non-zero beta value
docs/source/grpo_trainer.md	Added a Tip explaining the new default and its motivation

Comments suppressed due to low confidence (3)

tests/test_grpo_trainer.py:812

• The dedicated test for the beta=0.0 behavior was removed. It would be valuable to add a test that verifies the reference model is not loaded and no KL penalty is applied when beta is zero.

def test_training_beta_non_zero(self):

trl/trainer/grpo_config.py:136

• [nitpick] The previous warning about numerical instability for long training runs when beta=0.0 was removed. Consider re-adding a brief caution or linking to further guidance so users are aware of potential edge cases.

training speed.

trl/trainer/grpo_config.py:391

• Changing beta's default from 0.04 to 0.0 is a breaking change for existing users. Please document this change in the changelog or add a deprecation notice to help users migrate.

default=0.0,