Record: MLP3x + Int8 Tok Emb + Grouped LZMA + Sliding Window (val_bpb=1.1623)

[ChaseWNorton]

MLP3x + Int8 Tok Emb + Grouped LZMA + Sliding Window

This submission starts from the public 10-minute baseline family and makes three main changes:

1. Increase feedforward capacity from 2x to 3x.
2. Train and evaluate at seq_len=2048.
3. Use a custom grouped low-bit export plus sliding-window evaluation to improve the final under-cap score.

The model was trained for the official 600s wallclock limit on 8x H100 SXM, then repacked into a submission-valid artifact under the 16,000,000 byte limit.

Model

• VOCAB_SIZE=1024
• NUM_LAYERS=9
• MODEL_DIM=512
• NUM_HEADS=8
• NUM_KV_HEADS=4
• MLP_MULT=3
• TIE_EMBEDDINGS=1
• RoPE + RMSNorm + tied input/output embeddings
• U-Net-style skip structure inherited from the baseline

This keeps the backbone close to the baseline while spending more of the parameter budget on the MLP.

Training Setup

The timed run used:

• TRAIN_BATCH_TOKENS=786432
• TRAIN_SEQ_LEN=2048
• ITERATIONS=20000
• MAX_WALLCLOCK_SECONDS=600
• WARMUP_STEPS=20
• WARMDOWN_ITERS=3000
• TIED_EMBED_LR=0.03
• MATRIX_LR=0.02
• SCALAR_LR=0.02
• MUON_MOMENTUM=0.99

Logged optimizer summary:

• tie_embeddings:True embed_lr:0.03 head_lr:0.0 matrix_lr:0.02 scalar_lr:0.02

Logged attention summary:

• attention_mode:gqa num_heads:8 num_kv_heads:4

The script includes QAT support, but this specific timed run stopped before QAT activation:

• qat_enabled:True
• qat_start_frac:0.500
• qat_start_step:10000
• actual stop step: 7534

So the final reported result is from post-training repacking of the timed checkpoint rather than from a checkpoint that had entered the QAT phase.

Timed Training Result

The official training run stopped at the wallclock cap:

• step:7534/20000
• train_time:600120ms
• step_avg:79.65ms

Validation at stop:

• val_loss=1.9844
• val_bpb=1.1753

Other logged details:

• peak memory allocated: 16738 MiB
• peak memory reserved: 16944 MiB
• raw checkpoint size: 86099351 bytes

Export / Compression

The first export evaluated from the timed run used:

• int6 for most tensors
• fp16 token embedding passthrough
• fp16 passthrough for the last two c_k weights
• zlib

That version evaluated very well but was not submission-valid because it was over the size cap:

• total size: 16639274 bytes
• standard post-export score: 1.18101095
• sliding-window score: 1.16018011

The final submission-valid repack uses:

• grouped QGv3 serialization
• lzma compression
• int6 for most tensors
• int8 for tok_emb.weight
• no fp16 passthrough tensors

This change was enough to get back under the limit while preserving almost all of the sliding-window gain.

Final Submission Artifact

• artifact path: final_model.mixed_tok8_lzma.ptz
• compressor: lzma
• model bytes: 15845980
• code bytes: 64924
• total bytes: 15910904

This is submission-valid under the 16,000,000 byte cap.

Final Scores

Exact post-pack scores for the final under-cap artifact:

• standard eval:

  • val_loss=1.99867543
  • val_bpb=1.18372817

• sliding-window eval with seq_len=2048, stride=256:

  • val_loss=1.96250243
  • val_bpb=1.16230441

The submission score is therefore:

1.16230441 val_bpb

Notes

• The largest quality-preserving export change was keeping the token embedding at 8-bit while quantizing the rest of the model to 6-bit.
• Grouped serialization reduced overhead compared with a naive torch.save artifact.
• Fresh-load evaluation required keeping low-dimensional floating buffers, including RoPE frequency buffers, in fp32 to match the trained checkpoint behavior after reload.

Included Files

• README.md - this writeup
• submission.json - submission metadata
• train.log - exact log from the timed 8x H100 SXM run
• train_gpt.py - code snapshot for the submission artifact and evaluation path