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Sydney RunkleandGitHub
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## Summary Adds a Beta admonition to the `DeltaChannel` surface area so users can distinguish stable from in-progress contracts. Single-sourced on the base class; subclass overrides in `checkpoint-postgres` / `checkpoint-sqlite` / memory inherit the marker via their existing references back to the base. Touched: - `DeltaChannel` (`libs/langgraph/langgraph/channels/delta.py`) - `BaseCheckpointSaver.get_delta_channel_history` and `aget_delta_channel_history` (`libs/checkpoint/.../base/__init__.py`) - `DeltaChannelHistory` TypedDict - `CheckpointMetadata.delta_updates_since_snapshot` ## Why docstring admonitions, not `@beta` The base `get_delta_channel_history` methods are designed to be overridden by savers. Wrapping with `@beta` (from `langchain_core._api`) would emit warnings whenever a subclass called `super().get_delta_channel_history(...)` or whenever the default ancestor walk fired. Docstring-only keeps the signal advisory and noise-free. `_DeltaSnapshot` is already leading-underscore-private, so it implicitly signals "internal." ## Versioning note This intentionally stays a **minor** bump for the checkpoint releases (4.0 → 4.1, 3.0 → 3.1): - The new methods are strictly additive — defaults provided on the base, no signatures changed, no removed APIs. Third-party savers keep working without overriding anything. - The beta marker and the version bump do orthogonal jobs: semver answers "is this a breaking change?" (no), the marker answers "is this contract stable?" (no). - Bumping major now would consume the lever you want available for when the delta contract actually changes in a breaking way. ## Test plan - [ ] Docstring-only — no behavioral change - [x] `make format && make lint` clean in `libs/checkpoint` and `libs/langgraph`