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Working with the datasets library — load_dataset, .map() for tokenization, streaming, push to hub
Building a minimal inference server around an HF model (FastAPI + streaming) before reaching for TGI / vLLM
Do not use this skill when
Writing custom PyTorch training loops without HF abstractions — use the pytorch skill
Classical (non-DL) ML or tabular pipelines — use scikit-learn
LLM application orchestration (chains, agents, retrievers) — use langchain
Pure GPU kernel / numeric compute without neural-net structure — use cuda-python
Production deployment of LLMs at high throughput — TGI / vLLM / SGLang are dedicated servers; this skill covers the model side, not serving infra
Provider-API code (openai, ) that doesn't import — use the relevant SDK skill instead
anthropic
transformers
Purpose
HuggingFace Transformers is the model-definition framework for state-of-the-art text, vision, audio, and multimodal models. It exposes a unified from_pretrained loading API, the pipeline() quick-inference helper, AutoModelFor* task heads, Trainer for fine-tuning, and generate() for autoregressive decoding. Over a million model checkpoints on the Hub use the Transformers model definition, which downstream frameworks (vLLM, TGI, SGLang, Axolotl, Unsloth, DeepSpeed, FSDP, llama.cpp, mlx) read directly.
This skill codifies the patterns that matter for HF in production: device-aware loading (device_map="auto", dtype="auto"), attention-kernel selection (sdpa default, flash_attention_2 on supported GPUs), generation hygiene (max_new_tokens, padding_side="left" for batch generation, eos_token_id, streaming via TextIteratorStreamer), quantization recipes (bitsandbytes 4-bit NF4 + double-quant for QLoRA), PEFT/LoRA wiring with target_modules matched to the architecture, and Trainer configuration with the v5 names (eval_strategy, not evaluation_strategy; processing_class=tokenizer, not the legacy tokenizer= keyword).
Capabilities
Install and environment
Install transformers plus a backend (torch is canonical) and optional companions: datasets for data loading, accelerate for multi-GPU and quantization plumbing, peft for LoRA, bitsandbytes for 4/8-bit quantization on CUDA. Configure HF_HOME to control cache location; hf CLI (hf auth login) authenticates for gated models like Llama and Gemma. See references/setup.md.
Pipelines — quick inference
pipeline("task-name", model=..., device_map="auto", dtype="auto") is the fastest path from checkpoint to predictions. Task names cover text-generation, text-classification, token-classification (NER), summarization, translation, image-classification, audio-classification, automatic-speech-recognition, image-text-to-text, and many more. Pipelines accept batches as lists and support batch_size for throughput. See references/pipelines.md.
Tokenizers and chat templates
AutoTokenizer.from_pretrained(...) loads the matching tokenizer. Fast tokenizers (Rust-backed) are default; pass use_fast=False only if you need a Python-pure tokenizer. For batched encoding, pass padding=True, truncation=True, max_length=.... For chat models, tokenizer.apply_chat_template(messages, add_generation_prompt=True, return_tensors="pt") is the canonical way to build the prompt — never hand-format role tokens. See references/tokenizers.md.
Models — AutoModel families
AutoModelForCausalLM for LLMs, AutoModelForSequenceClassification for text classification, AutoModelForTokenClassification for NER, AutoModelForSeq2SeqLM for encoder-decoder (T5, BART), AutoModelForSpeechSeq2Seq for Whisper, AutoModelForImageTextToText for VLMs. Load with dtype=torch.bfloat16 (or "auto"), device_map="auto", attn_implementation="sdpa". See references/models.md.
Generation — .generate() API
The decoding entry point. Key kwargs: max_new_tokens (always set — max_length includes prompt), do_sample, temperature, top_p, top_k, repetition_penalty, num_beams, eos_token_id, pad_token_id. Wrap reusable configs in GenerationConfig. For batch generation set tokenizer.padding_side = "left". Stream tokens with TextIteratorStreamer running model.generate on a background thread. See references/generation.md.
Quantization
BitsAndBytesConfig(load_in_4bit=True, bnb_4bit_quant_type="nf4", bnb_4bit_compute_dtype=torch.bfloat16, bnb_4bit_use_double_quant=True) is the QLoRA-ready recipe. Pass via from_pretrained(..., quantization_config=...). GPTQ, AWQ, and quanto are alternatives for inference-only deployment. See references/quantization.md.
Fine-tuning with Trainer
Trainer(model, args, train_dataset, eval_dataset, processing_class=tokenizer, data_collator=..., compute_metrics=...) runs the whole loop. TrainingArguments keys you will set: output_dir, per_device_train_batch_size, gradient_accumulation_steps, learning_rate, num_train_epochs, eval_strategy, save_strategy, logging_steps, bf16=True, gradient_checkpointing=True, push_to_hub=True. Distributed via fsdp="full_shard" or deepspeed="ds_config.json". See references/fine-tuning-trainer.md.
PEFT — LoRA and QLoRA
peft is a separate package. LoraConfig(r=16, lora_alpha=32, lora_dropout=0.05, target_modules=["q_proj","v_proj"], task_type="CAUSAL_LM") + get_peft_model(base_model, config) returns a wrapped model with ~1% trainable params. QLoRA = bitsandbytes 4-bit base + LoRA adapters on top. After training, merge_and_unload() produces a single deployable checkpoint. See references/peft-and-lora.md.
Datasets
from datasets import load_dataset; ds = load_dataset("squad"). Tokenize via ds.map(tokenize_fn, batched=True, remove_columns=...). Use streaming=True for datasets larger than disk. train_test_split, filter, select, shuffle, and push_to_hub round out the surface. See references/datasets.md.
Multimodal — vision and audio
Image-text models (LLaVA, Idefics3, Qwen-VL, InternVL) use AutoProcessor for unified text+image preprocessing and AutoModelForImageTextToText for inference. Pass images as PIL, URL, or local path inside the chat message structure. Audio: Whisper via automatic-speech-recognition pipeline, or AutoModelForSpeechSeq2Seq + AutoProcessor for finer control. See references/multimodal.md.
Inference servers
For high-throughput LLM serving, TGI (HuggingFace) and vLLM are the standard choices — both read Transformers model definitions. For a minimal in-process server, wire AutoModelForCausalLM behind FastAPI with StreamingResponse and TextIteratorStreamer. See references/inference-server.md.
Troubleshooting
CUDA OOM during .generate() — reduce batch, quantize to 4-bit, ensure use_cache=True, drop attn_implementation from eager to sdpa. Tokenizer padding error — set tokenizer.pad_token = tokenizer.eos_token. Slow generation — switch to sdpa or flash_attention_2. Gated-model 403 — hf auth login and accept terms. trust_remote_code=True warning — only enable for checkpoints you trust. See references/troubleshooting.md.
Behavioral Traits
Always load model and tokenizer from the same checkpoint string in the same code block — mismatched vocab silently produces garbage
Always set max_new_tokens on .generate() calls — never rely on max_length (which includes prompt) for new code
Always call tokenizer.apply_chat_template(messages, add_generation_prompt=True, ...) for chat-tuned models — never concatenate role tokens manually
Always set tokenizer.padding_side = "left" before batched generation; decoder-only models attend right-to-left, right-padding corrupts output
Always pass device_map="auto" and dtype="auto" (or an explicit torch.bfloat16) on first load — let accelerate place tensors
Prefer attn_implementation="sdpa" as the safe default; opt into "flash_attention_2" only on Ampere/Hopper with the package installed
Prefer eval_strategy="steps" with a small eval_steps for long runs so you see loss curves early
Prefer LoRA over full fine-tune when target task fits — orders of magnitude less VRAM, comparable quality
When debugging generation, run once with do_sample=False (greedy) — sampling masks systematic prompt-format bugs
When training is OOM, the first knob is gradient_accumulation_steps, second is gradient_checkpointing=True, third is quantization + LoRA
In Trainer code, pass the tokenizer/processor as processing_class=... — the legacy tokenizer= keyword still works but is deprecated
Important Constraints
NEVER pad on the right when generating with a decoder-only LLM — set tokenizer.padding_side = "left"
NEVER call .generate() inside an autograd context — wrap in torch.inference_mode() or torch.no_grad() to avoid leaking the graph
NEVER mix the model's dtype with manual .half() / .bfloat16() calls when dtype=... and device_map="auto" are already set — accelerate already placed and cast the modules
NEVER pass trust_remote_code=True to a checkpoint you do not control or have not audited — it executes arbitrary Python on import
NEVER use max_length to bound new tokens — it includes the prompt; use max_new_tokens
NEVER assume the tokenizer has a pad_token — many causal LMs ship without one; set tokenizer.pad_token = tokenizer.eos_token before batching
NEVER use the legacy torch_dtype= kwarg in new code — the supported keyword in current Transformers is dtype=
NEVER use the legacy evaluation_strategy= kwarg in TrainingArguments — it is eval_strategy=
NEVER full-fine-tune a 7B+ model on a single consumer GPU — use QLoRA (4-bit base + LoRA adapters) instead
ALWAYS log in with hf auth login before loading gated checkpoints (Llama, Gemma, Mistral-Instruct) or pre-fetch them in CI with HF_TOKEN
ALWAYS save the tokenizer alongside the model when checkpointing — tokenizer.save_pretrained(out_dir) next to model.save_pretrained(out_dir)
Related Skills
Parent
python — language baseline (this skill assumes Python 3.11+ comfort with type hints and venv)
Foundation
pytorch — DL backend; Transformers is built on top of torch.nn.Module and reuses tensor / autograd / AMP primitives
GPU environment
cuda-python — CUDA driver/runtime, device detection, GPU/CPU fallback patterns referenced when configuring bitsandbytes and flash_attention_2
Adjacent
pydantic — typed structured outputs from LLM generations; pair with apply_chat_template and a JSON-schema-constrained decoder
pytest — unit tests for tokenization, prompt construction, and generation determinism (set do_sample=False, fixed seed)
API Reference
Domain-specific references (Pattern 2) — load only what's relevant:
Topic
File
Index, decision map — task → model class → pipeline → reference file
