{
  "experiment": "Gemma 4 V4 input-variation SAE (bnb 4-bit)",
  "caveat_quantization": "4-bit quantized inference; results characterize quantized checkpoint.",
  "prompt_equivalence": "DIAGNOSTIC ONLY: inputs DIFFER across neutral / V0 / V3 templates. This SAE is an input-classifier baseline, NOT a behavior detector. Cohen's d here captures input-template separability, not generation-process separability.",
  "model": {
    "key": "gemma4_e2b",
    "hf_name": "google/gemma-4-E2B",
    "d_in": 1536,
    "layer": 25,
    "quantization": "bnb 4-bit nf4 double_quant fp16_compute"
  },
  "sae": {
    "architecture": "topk",
    "k": 32,
    "d_sae": 6144,
    "metrics": {
      "mse_loss": 0.014618407003581524,
      "explained_variance": 0.9957529839731779,
      "l0": 32.0,
      "alive_features": 394,
      "train_time_s": 109.1,
      "num_activations": 3619,
      "final_epoch_loss": 0.015443
    },
    "checkpoint": "gemma4_e2b_v4input_topk_k32_L25_bnb4bit.pt"
  },
  "input_split": {
    "n_neutral": 50,
    "n_v0": 50,
    "n_v3": 50,
    "neutral_vs_v0_block": {
      "label": "input_neutral_vs_v0",
      "d_max": 1.4726576805114746,
      "d_mean": 0.005705477204173803,
      "d_above_1": 11,
      "d_above_2": 0,
      "top10_ids": [
        2186,
        5437,
        3069,
        2291,
        6081,
        2928,
        3815,
        2731,
        4617,
        1613
      ],
      "top10_d": [
        1.4726576805114746,
        1.43470299243927,
        1.3176182508468628,
        1.3077726364135742,
        1.2976280450820923,
        1.2607280015945435,
        1.245164394378662,
        1.2348037958145142,
        1.151690125465393,
        1.1124372482299805
      ]
    },
    "neutral_vs_v3_block": {
      "label": "input_neutral_vs_v3",
      "d_max": 2.9800453186035156,
      "d_mean": 0.007209507282823324,
      "d_above_1": 12,
      "d_above_2": 3,
      "top10_ids": [
        3815,
        1703,
        5437,
        2731,
        2291,
        2186,
        3686,
        5465,
        1931,
        3069
      ],
      "top10_d": [
        2.9800453186035156,
        2.5605528354644775,
        2.048558473587036,
        1.9496744871139526,
        1.8200923204421997,
        1.6280057430267334,
        1.5141710042953491,
        1.4185123443603516,
        1.3666783571243286,
        1.3026963472366333
      ]
    }
  },
  "timestamp": "2026-04-21T06:53:37.744242+00:00"
}