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* [core] Shard tensor-parallel checkpoints on load and save Stream each rank's slice of a tensor-parallel checkpoint straight off disk instead of materializing the full checkpoint on every rank and resharding it afterwards, and gather the shards back on save. - `from_pretrained(..., parallel_config=TensorParallelConfig(...))` resolves the shard specs on the still-meta model, then slices each safetensors tensor before the dtype cast, so host memory peaks at ~1/tp_degree of the checkpoint. - `save_pretrained` all-gathers the DTensors into an ordinary checkpoint, or writes a distributed checkpoint with `dcp=True` so no full tensor is ever formed. The writing `tp_degree` is recorded, since a packed weight's stored layout is interleaved by it. - Factor the plan interpretation out of the Neuron pre-shard path into shared `TPShardSpec` / `resolve_tp_shard_specs` / `_local_shard` / `_hooks_only_styles` helpers, so both backends and both the load and save paths shard identically. * Raise when tensor parallelism is combined with quantization, offloading or LoRA Addresses the remaining two items of the review on #13718: tensor parallelism was rejected alongside quantization and `device_map` only on the `from_pretrained` streaming path, while `enable_parallelism` — which the quantization error message itself recommended — accepted a quantized, offloaded or adapter-injected model and sharded it anyway. - Add `_check_tp_model_state`, called from `apply_tensor_parallel`, the one chokepoint every TP entry point funnels through. It rejects a model that is quantized, group-offloaded, placed by accelerate (`device_map` or CPU offload), or has PEFT layers injected. Placed before the device-type check so the reported reason is the useful one. - Guard the reverse order too: `enable_group_offload`, the two pipeline CPU-offload methods, and `load_lora_adapter` now refuse a tensor-parallel model. - `save_pretrained` refuses a quantized tensor-parallel model. Previously the `dcp=True` branch returned before the quantizer's serialization step, writing shards with no quantization metadata and no error. - The DCP load guard checked the `quantization_config` kwarg only, so a pre-quantized checkpoint directory loaded silently; check the config's own entry too, and add the missing `_tp_plan` check that otherwise surfaced as a raw `AttributeError`. - Correct the `from_pretrained` message and the doc sentence that pointed at `enable_parallelism` as a way to shard a quantized model. The new tests are the first tensor-parallel tests that need neither an accelerator nor more than one rank: every case asserts a raise before any collective, so they run single-process on gloo. * review: remove tp save/ dcp related * review: add a new helper . * review: moved the TP checks into enable_parallelism * review: move the warning under caution block * review: add loading time numbers * review: move tp size dividende check * review: delete test * review: consolidate tp checks * review: consolidate the tp checks, all in tensor_parallel.py * review: improve conditionals * review: debug info * review: check weights format before instantiating the model * review: restore duplicated _find_mismatched_keys since irrelevant * revert: delete duplicated helper * review: update doc for loading benchmark of flux2-dev * review: improve the raising check * review: add an args section * Test tensor-parallel loading from sharded checkpoints --------- Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>