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KO

From scratch with a 5080

·2026.04.22 01:32

Key point

Trained a 235M-parameter LLM from scratch using a single RTX 5080.

Details

Trained a 235M-parameter LLM from scratch in PyTorch without pretrained weights.

The architecture consists of 18 layers, hidden size 1024, GQA 16 query heads / 4 KV heads, SwiGLU FFN 2816, RoPE (theta 10000), RMSNorm pre-norm, tied embeddings, and uses a 32k SentencePiece BPE vocab.

Training was fit onto a single consumer GPU, the RTX 5080, using bf16 mixed precision and gradient checkpointing, training on about 5B tokens at seq len 1024.

The data pipeline was also built from scratch.

  • Used FineWeb-Edu, Wikipedia, StackExchange, code, ArXiv
  • Quality and toxicity filtering
  • MinHash deduplication
  • Custom SentencePiece tokenizer
  • Domain-weighted mixing
  • Pretraining plus instruction tuning, with loss masking applied so only assistant tokens are trained on

Sample outputs were also shared. In the examples, it answered 1914 for a "World War 1" question, and gave a reasonable response to the definition of steak.

The next version, Plasma 1.1, is currently being trained at 500M parameters, aiming for better multi-turn conversation, a larger vocab, and byte fallback.

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