Add submission: QAT Int5/Int6 + Backout + BigramHash + SWA50 (val_bpb=1.1477)

Author: gowtham0992

records/track_10min_16mb/2026-03-20_QAT_Int5Int6_BigramHash_Backout_SWA50/README.md

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+# QAT Int5/Int6 + Backout + U-Net Skips + BigramHash(10240) + SWA50
+
+**val_bpb: 1.1477** (seed=42, sliding window stride=64, post int5/int6+zstd quantization roundtrip, 15.94 MB)
+
+## Run Command
+
+```bash
+pip install zstandard  # optional but recommended for better compression
+torchrun --standalone --nproc_per_node=8 train_gpt.py
+```
+
+All parameters are set as defaults in `train_gpt.py`. No env vars needed.
+Falls back to zlib if zstandard is not installed.
+
+## Key Techniques
+
+### Quantization-Aware Training (QAT)
+During training, large weight matrices pass through a simulated quantization bottleneck using the
+straight-through estimator (STE). MLP weights see int5 noise, attention weights see int6 noise.
+The model learns to be robust to quantization, reducing the post-quant penalty from ~0.016 BPB
+to ~0.005 BPB — roughly 0.01 BPB free compared to post-training quantization alone.
+
+### Backout (Learned Residual Subtraction)
+A learned scalar λ (init=0.2) subtracts the midpoint layer's activation from the final output:
+`x = x - λ * x_mid`. Prevents over-reliance on early representations.
+
+### U-Net Skip Connections
+Encoder-decoder structure (5+5 layers) with learned per-dimension skip weights connecting
+encoder to decoder layers.
+
+### SVD Embedding Initialization
+Tied embeddings initialized via SVD spectral decay: singular values reshaped to follow a
+1/√k profile for better initial token representations.
+
+### Mixed Int5/Int6 Quantization + zstd-22
+- Int5 [-16,15] for MLP weights (most compressible)
+- Int6 [-32,31] for attention weights (precision-sensitive)
+- FP16 for tied embeddings and last-2-layer key projections (Late-K)
+
+### BigramHash(10240) + SmearGate
+Hash consecutive token pairs into 10240-bucket embedding table (dim=128, projected to 512).
+SmearGate blends each token with the previous token's embedding.
+
+### Stochastic Weight Averaging
+SWA every 50 steps during warmdown (start_frac=0.4). Smoother weight distributions quantize better.
+
+## Architecture
+- 10 layers, 512 dim, 8 heads, 4 KV heads (GQA)
+- MLP 3x expansion (hidden=1536), relu² activation
+- Tied embeddings, logit softcap=30
+- Orthogonal init with muP-scaled output projections
+
+## Hyperparameters
+
+| Parameter | Value |
+|-----------|-------|
+| matrix_lr (Muon) | 0.02 |
+| scalar_lr (AdamW) | 0.02 |
+| tied_embed_lr | 0.03 |
+| muon_weight_decay | 0.04 |
+| adamw_weight_decay | 0.01 |
+| warmdown_iters | 3000 |
+| swa_every / start_frac | 50 / 0.4 |
+| prune_frac | 0.08 |
+| eval_stride | 64 |
+| compressor | zstd-22 |
+
+Built on PR #162 by @unnir (SmearGate, BigramHash, OrthoInit) and techniques from @thwu1 and @raahilshah.

records/track_10min_16mb/2026-03-20_QAT_Int5Int6_BigramHash_Backout_SWA50/submission.json

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+{
+  "name": "QAT Int5/Int6 + BigramHash(10240) + Backout + SWA50 + U-Net Skips",
+  "val_loss": 1.93785918,
+  "val_bpb": 1.14770936,
+  "bytes_total": 15935368,
+  "blurb": "Quantization-Aware Training (straight-through estimator) with int5 MLP / int6 attention. BigramHash 10240, SmearGate, Backout (learned residual subtraction), U-Net skip connections, SVD embedding init. Simple Muon + compiled Newton-Schulz5. SWA every 50 steps (start_frac=0.4). 8% magnitude pruning + zstd-22.",
+  "author": "gowtham0992",
+  "github_id": "gowtham0992",
+  "date": "2026-03-20"
+}