The Transformer

Layer 3 · Code

The Transformer

Assemble a full GPT-style transformer block and forward pass from scratch in PyTorch, and verify parameter counts against a real model.

15 min read110 XP

  1. RMSNorm

    a lighter-weight LayerNorm variant

  2. Attention sublayer

    reuse the module from the attention star

  3. MLP sublayer

    expand, activate, project down

  4. Full block

    pre-LN residual wiring around both

  5. Full model

    embeddings + N blocks + output head

Building the complete architecture bottom-up.

Start with the two primitives every modern block needs beyond attention: RMSNorm (the normalization most current models use instead of LayerNorm, since it drops the mean-centering step and is cheaper) and the MLP.