README.md

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license: apache-2.0
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 Playbox RFT Checkpoint (Generalist Base)

 
Model Name: Playbox_RFT_Checkpoint

Base Architecture: Qwen3.5-0.8B-Base (24 transformer layers, mixed linear/full attention, hidden dimension 1024, grouped-query attention).

Parameters: ~0.8B

Developers: Epoch AI Labs

Intended Use: General mathematical reasoning, chain-of-thought generation, and pattern completion. Serves as the default, untouched path for standard mathematical queries (e.g., GSM8K) in the Routed Hammer ensemble.

Training Pipeline:
Stage 1 (Full-Parameter SFT): Supervised fine-tuning on GSM8K training data to establish reasoning chains and formatting.

Stage 2A (Periphery-Only GRPO): Group Relative Policy Optimization restricted to the final 8 transformer layers to preserve lower-layer capabilities while improving math output. Utilized strict math gating and frontier filtering.

Stage 2B (Identity GRPO Alignment): Final 6 layers trained on behavioral objectives (identity, anti-sycophancy, ambiguity handling) with no math training.


Performance:

GSM8K: 50.3% accuracy, 94.8% format compliance (outperforming comparators up to 9× its size like Qwen2.5-Math-7B-Instruct).

Adversarial OOD: 22.0% accuracy (without routing).



Limitations: Vulnerable to catastrophic forgetting. If fine-tuned further on tool-integrated reasoning (TIR), it completely loses general mathematical ability (dropping to 3.5% on out-of-distribution math). Behavioral alignment (identity) remains unsolved (0% preservation).