Add xlstm model (#39665)

* Add xLSTM cleanly with optimizations.

* Fix style.

* Fix modeling test.

* Make xLSTM package optional.

* Fix: Update torch version check.

* Fix: Bad variable naming in test.

* Fix: Import structure cleaning with Ruff.

* Fix: Update docstrings.

* Fix: Mitigate unused config attr tests by explicit usage.

* Fix: Skip tests, if xlstm library is not installed.

* Feat: Enable longer context window for inference by chunking.

* Fix: Make training test pass by lowering target accuracy.

* Chore: Increase test verbosity for failing generation test.

* Update docs/source/en/model_doc/xlstm.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Fix: Make xlstm available even without CUDA.

* Chore: Remove unnecessary import.

* Fix: Remove BOS insertion.

* Chore: Improve xLSTMCache documentation.

* Integrate basic xLSTM fallback code.

* Chore: Remove unnecessary import.

* Chore: Remove duplicate LayerNorm.

* chore: update copyright, minor reformatting

* fix: refactor mLSTMStateType due to missing torch import

* fix: add missing import

* Chore: Replace einops.

* fix: apply ruff formatting

* fix: run `make fix-copies` to re-generate dummy_pt_objects.py

* fix: make type hints Python 3.9 compatible

* fix: remove obsolete import

* fix: remove obsolete method from docs

* chore: remove obsolete `force_bos_token_insert` from config

* Chore: Remove duplicated xLSTMCache class.

* Fix: Formatting of modeling_xlstm.py

* Chore: Remove xlstm package requirement from test. Re-add update_rnn_state.

* Fix: Update xLSTMCache docstring.

* Feat: Add proper initialization of xLSTM.

* Chore: Re-format files.

* Chore: Adapt format.

* Fix: xLSTMCache import restructuring.

* Fix: Add __all__ lists to modeling and configuration files.

* Chore: Reformat.

* Fix: Remove unnecessary update_rnn_state function.

* Fix: Undo test accuracy quickfix.

* Fix: Update copyright year, remvoe config copy.

* Chore: Flatten all internal configs to xLSTMConfig.

* Fix: Unused config variables check.

* Chore: Remove unnecessary imports.

* Fix: Unify xlstm cache argument from batch_size to max_batch_size.

* Chore: Remove bad default arg value for xLSTMCache.

* Chore: Rename core configuration arguments to HF default in xLSTM.

* Chore: Fix formatting.

* Fix: xLSTM Cache config access.

* Fix: Update xlstm tests for config update.

* Feat: Re-add embbeding_dim, num_blocks config options for compat with xLSTM-7B.

* Fix: Configuration xLSTM python3.9 syntax.

* Fix: Difference to main in test_utils.py assertion.

* Fix: Bad syntax in xlstm config for python3.9.

* Fix: xLSTMConfig docstring.

* Fix: xLSTMConfig docstring.

* Fix typing issues in xLSTM and BeiT, Paligemma.

* Fix: Exclude xLSTM from test cache utils.

* Chore: Fix style.

* Chore: Fix format.

* Chore: Remove unnecessary LayerNorm, NormLayer layer abstractions.

* Chore: Remove asserts and replace with ValueErrors.

* Chore: Update __init__.py structure of xLSTM.

* Chore: Clean xLSTM initialization of weights.

* Fix index names in modeling_xlstm.py

* Update xlstm model test typing annotations.

* Fix: Remove all asserts.

* Revert changes to the main __init__.py

* Fix: Move xLSTMCache to modeling_xlstm.py

* Fix: Remove xLSTMForCausalLM mapping from modeling_auto.py

* Remove xLSTMCache from dummy_pt_objects.py

* Fix: Remove extended torchdynamo compilation check integrating cuda graph captures.

* Revert test_cache_utils.py xLSTM change.

* Fix: Move xLSTM init functions before init call.

* Remove xLSTMCache from generation utils.

* Fix: Clean xLSTM init functionality for recursive calls.

* Fix: Move xLSTMCache before its first call.

* Fix formatting.

* Add partial docstring for xLSTMModel forward.

* Fix xLSTMCache docstring in xLSTMModel.

* Remove xLSTMCache from public documentation. Update auto_docstring.

* Remove all agressive shape comments

* style

* Fix names

* simplify

* remove output_hidden_states

* Update modeling_xlstm.py

* Update modeling_xlstm.py

* Update test_modeling_xlstm.py

* Update modeling_xlstm.py

* Update modeling_xlstm.py

* fix

* fix

* style

* style

---------

Co-authored-by: Korbinian Poeppel <korbinian.poeppel@nx-ai.com>
Co-authored-by: Korbinian Pöppel <37810656+kpoeppel@users.noreply.github.com>
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
Co-authored-by: Sebastian Böck <sebastian.boeck@nx-ai.com>
Co-authored-by: Korbinian Poeppel <poeppel@ml.jku.at>

docs/source/en/_toctree.yml

@@ -697,6 +697,8 @@
         title: XLM-V
       - local: model_doc/xlnet
         title: XLNet
+      - local: model_doc/xlstm
+        title: xLSTM
       - local: model_doc/yoso
         title: YOSO
       - local: model_doc/zamba

docs/source/en/model_doc/xlstm.md

@@ -0,0 +1,47 @@
+<!--Copyright 2025 NXAI GmbH. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+the License. You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+specific language governing permissions and limitations under the License.
+
+⚠️ Note that this file is in Markdown but contain specific syntax for our doc-builder (similar to MDX) that may not be
+rendered properly in your Markdown viewer.
+
+-->
+
+
+# xLSTM
+
+## Overview
+
+The xLSTM model was proposed in [xLSTM: Extended Long Short-Term Memory](https://openreview.net/forum?id=ARAxPPIAhq) by Maximilian Beck*, Korbinian Pöppel*, Markus Spanring, Andreas Auer, Oleksandra Prudnikova, Michael Kopp, Günter Klambauer, Johannes Brandstetter and Sepp Hochreiter.
+xLSTM updates the original LSTM architecture to be competitive with Transformer models by introducing exponential gating, matrix memory expansion, and parallelizable training and ingestion.
+
+The [7B model](https://hf.co/NX-AI/xLSTM-7b) variant was trained by the xLSTM team Maximilian Beck, Korbinian Pöppel, Phillip Lippe, Richard Kurle, Patrick Blies, Sebastian Böck and Sepp Hochreiter at NXAI.
+
+The abstract from the paper is the following:
+
+*In the 1990s, the constant error carousel and gating were introduced as the central ideas of the Long Short-Term Memory (LSTM). Since then, LSTMs have stood the test of time and contributed to numerous deep learning success stories, in particular they constituted the first Large Language Models (LLMs). However, the advent of the Transformer technology with parallelizable self-attention at its core marked the dawn of a new era, outpacing LSTMs at scale. We now raise a simple question: How far do we get in language modeling when scaling LSTMs to billions of parameters, leveraging the latest techniques from modern LLMs, but mitigating known limitations of LSTMs? Firstly, we introduce exponential gating with appropriate normalization and stabilization techniques. Secondly, we modify the LSTM memory structure, obtaining: (i) sLSTM with a scalar memory, a scalar update, and new memory mixing, (ii) mLSTM that is fully parallelizable with a matrix memory and a covariance update rule. Integrating these LSTM extensions into residual block backbones yields xLSTM blocks that are then residually stacked into xLSTM architectures. Exponential gating and modified memory structures boost xLSTM capabilities to perform favorably when compared to state-of-the-art Transformers and State Space Models, both in performance and scaling.*
+
+This model was contributed by [NX-AI](https://huggingface.co/NX-AI).
+The original code can be found [here](https://github.com/NX-AI/xlstm).
+
+
+## xLSTMConfig
+
+[[autodoc]] xLSTMConfig
+
+## xLSTMModel
+
+[[autodoc]] xLSTMModel
+    - forward
+
+## xLSTMLMHeadModel
+
+[[autodoc]] xLSTMForCausalLM
+    - forward