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transformers/docs/source/en/model_doc/longcat_flash.md

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+*This model was released on 2025-09-01 and added to Hugging Face Transformers on 2025-09-17.*
+
+# LongCatFlash
+
+## Overview
+
+The LongCatFlash model was proposed in [LongCat-Flash Technical Report](https://huggingface.co/papers/2509.01322) by the Meituan LongCat Team.
+LongCat-Flash is a 560B parameter Mixture-of-Experts (MoE) model that activates 18.6B-31.3B parameters dynamically (average ~27B). The model features a shortcut-connected architecture enabling high inference speed (>100 tokens/second) and advanced reasoning capabilities.
+
+The abstract from the paper is the following:
+
+*We present LongCat-Flash, a 560 billion parameter Mixture-of-Experts (MoE) language model featuring a dynamic computation mechanism that activates 18.6B-31.3B parameters based on context (average ~27B). The model incorporates a shortcut-connected architecture enabling high inference speed (>100 tokens/second) and demonstrates strong performance across multiple benchmarks including 89.71% accuracy on MMLU and exceptional agentic tool use capabilities.*
+
+Tips:
+
+- LongCat-Flash uses a unique shortcut-connected MoE architecture that enables faster inference compared to traditional MoE models
+- The model supports up to 128k context length for long-form tasks
+- Dynamic parameter activation makes it computationally efficient while maintaining high performance
+- Best suited for applications requiring strong reasoning, coding, and tool-calling capabilities
+- The MoE architecture includes zero experts (nn.Identity modules) which act as skip connections, allowing tokens to bypass expert computation when appropriate
+
+This model was contributed by [Molbap](https://huggingface.co/Molbap).
+The original code can be found [here](https://huggingface.co/meituan-longcat/LongCat-Flash-Chat).
+
+## Usage examples
+
+The model is large: you will need 2x8 H100 to run inference.
+
+```python
+# launch_longcat.py
+from transformers import LongcatFlashForCausalLM, AutoTokenizer
+import torch
+
+model_id = "meituan-longcat/LongCat-Flash-Chat"
+
+tokenizer = AutoTokenizer.from_pretrained(model_id)
+
+chat = [
+      {"role": "user", "content": "Hello! What is the capital of France? What can you tell me about it?"},
+]
+
+model = LongcatFlashForCausalLM.from_pretrained(
+      model_id,
+      tp_plan="auto",
+      dtype=torch.bfloat16,
+      )
+
+inputs = tokenizer.apply_chat_template(
+      chat, tokenize=True, add_generation_prompt=True, return_tensors="pt").to(model.device)
+
+outputs = model.generate(inputs, max_new_tokens=30)
+print(tokenizer.batch_decode(outputs))
+```
+
+To run with TP, you will need torchrun:
+
+```bash
+torchrun  --nproc_per_node=8 --nnodes=2 --node_rank=0 | 1  --rdzv-id <an_id> --rdzv-backend c10d --rdzv-endpoint $NODE_ID:$NODE_PORT  --log-dir ./logs_longcat launch_longcat.py
+```
+
+And you'll get a nice generation:
+
+```json
+[Round 0] USER:Hello! What is the capital of France? What can you tell me about it? ASSISTANT:Hello! 😊 The capital of France is Paris, one of the most famous and beloved cities in the world. Here’s a quick overview of what makes Paris special:
+1. Iconic Landmarks
+
+    Eiffel Tower – The global symbol of France, built in 1889 for the World's Fair.
+    Notre-Dame Cathedral – A masterpiece of Gothic architecture (currently under restoration after the 2019 fire).
+    Louvre Museum – The world’s largest art museum, home to the Mona Lisa and Venus de Milo.
+    Sacré-Cœur Basilica – A stunning white church atop Montmartre with panoramic views.
+    Arc de Triomphe – Honors French military victories, with the Tomb of the Unknown Soldier beneath it.
+    Champs-Élysées – A glamorous avenue leading to the Arc de Triomphe, lined with shops and cafés.
+
+2. Culture & Arts
+
+    Paris is the "City of Light" (La Ville Lumière), a nickname from its early adoption of street lighting and its role as a center of enlightenment.
+    It’s a global hub for fashion (haute couture, Paris Fashion Week) and art (Impressionism, Picasso, Dali).
+    Famous literary figures like Hemingway, Fitzgerald, and Sartre lived and wrote here.
+
+3. Food & Cuisine
+
+    Croissants, baguettes, macarons, and crème brûlée are just a few of its culinary delights.
+    Paris has over 100 Michelin-starred restaurants and countless cozy bistros.
+    The Marché d’Aligre and Rue Mouffetard are great for fresh produce and local flavors.
+
+4. History & Politics
+
+    Founded in the 3rd century BC by the Parisii tribe, it became a major European city under the Romans.
+    The French Revolution (1789–1799) began here, leading to the fall of the monarchy.
+    Today, it’s the political and economic heart of France, housing the French President’s residence (Élysée Palace) and the National Assembly.
+
+**
+```
+
+## LongcatFlashConfig
+
+[[autodoc]] LongcatFlashConfig
+
+## LongcatFlashPreTrainedModel
+
+[[autodoc]] LongcatFlashPreTrainedModel
+    - forward
+
+## LongcatFlashModel
+
+[[autodoc]] LongcatFlashModel
+    - forward
+
+## LongcatFlashForCausalLM
+
+[[autodoc]] LongcatFlashForCausalLM