Highlights

• Ray Data: We added fixes for several to_pandas regressions introduced in 2.56: an opt-out flag (RAY_DATA_ENABLE_ARROW_BACKED_PANDAS_CONVERSION) for Arrow-backed conversion, an int64/double[pyarrow] overflow crash on concatenation, and a TensorDtype.__from_arrow__ crash on empty tensor columns (#64793, [#64794]).
• Ray Core: We added early detection for system-slice memory pressure: the memory monitor now snapshots the user and system cgroup slices together and logs an error when the system slice exceeds reserved system memory, warning users to raise --system-reserved-memory before it causes node deaths (#64492).
• Ray Serve: We added protobuf 7 compatibility and a routing fix for LLM direct streaming, so body-aware routers like PrefixCacheAffinityRouter no longer hang when RAY_SERVE_LLM_ENABLE_DIRECT_STREAMING=1 (#64592, [#64488]).

Ray Data

🔨 Fixes

• Fixed two Arrow-backed to_pandas regressions: added DataContext.enable_arrow_backed_pandas_conversion as an opt-out, and reconciled divergent numeric column types before concatenation to avoid int64/double[pyarrow] overflow crashes (#64793, [#64768]).
• Fixed a TensorDtype.__from_arrow__ crash on zero-size tensor elements by using an explicit row count instead of numpy's -1 dimension inference (#64794, [#64767]).
• Fixed a crash in hash partition caused by read-only hash arrays (#64584, [#64552], [#64559]).
• Nullified _input_dependencies in _get_args so exporting operator args no longer triggers an exponential sanitize_for_struct call chain over fused operators (#64412, [#64316]).

Ray Serve

🔨 Fixes

• Added protobuf >=7 compatibility to _proto_to_dict by binding to FieldDescriptor.is_repeated when the deprecated label attribute is absent (#64592, [#64362]).

Ray LLM

🔨 Fixes

• Fixed direct-streaming routing for body-aware routers: the ingress now parses the raw request body into a SimpleNamespace over routing-key fields (messages, prompt) so choose_replica receives the message body instead of raw bytes (#64488, [#64328], [#64326]).

Ray RLlib

🔨 Fixes

• Upgraded the ONNX example from the retired MobileNet v1 to MobileNet v3 via torchvision and pinned onnxscript in the GPU/ml-build CI dep locks, fixing ONNX export failures (#64591, [#64028], [#64031], [#64590], [#64033]).

Ray Core

💫 Enhancements

• The threshold memory monitor now snapshots both the user and system cgroup slices and logs an error when system-slice usage exceeds the reserved system memory, prompting users to raise --system-reserved-memory (#64492).

🔨 Fixes

• Disabled NCCL cuMem host buffer registration in CI pytests to stabilize GPU test runs (#64580, [#64146]).

Documentation

📖 Documentation

• Repointed the ASHA Tune example links to the renamed README document, fixing the fail_on_warning ReadTheDocs build on the release line (#64761, [#64630]).
• Updated the Python 3.10 CPU pip freeze dependency list for the Ray 2.56.0 release (#64447, [#64357]).