Ray-2.56.1

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).