Model loaded but tokenizer vocab size mismatch

When the model's config.json declares vocab size X but the tokenizer's vocab.json/tokenizer.json has size Y, transformers refuses to load. Causes:

• Partial download (one file missing)
• Mixed files from different model versions in the same directory
• A LoRA-merged model where the merge process didn't update the config

Re-download the full model to a fresh directory:

hf download meta-llama/Llama-3.1-8B-Instruct --local-dir ./llama-31-8b-clean

If you're sure the files are right but vocab is mismatched (rare, happens with custom-trained models), fix manually:

from transformers import AutoConfig, AutoTokenizer
tok = AutoTokenizer.from_pretrained("./your-model")
config = AutoConfig.from_pretrained("./your-model")
config.vocab_size = len(tok)  # match config to tokenizer
config.save_pretrained("./your-model")

Common after LoRA merging. When you merge a LoRA back into the base, both vocab.json AND config.json need to be the BASE model's files (the LoRA adapter has neither). Don't mix-and-match from different stages of training.