TheoBERT Base

theo-bert-base is a domain-specialized masked language model for biblical and theological text. It is a custom bidirectional encoder pretrained from scratch on bible and closely related doctrinal material, exported in a Hugging Face–compatible format.

This repository ships the MLM-shaped artifact: an encoder body paired with a working MLM head. It is the right checkpoint if you want fill-mask, token-level scoring, or a strong base for further domain-specific fine-tuning where token-level prediction matters.

What This Model Is For

Recommended use cases:

• Masked token prediction and token-level scoring in biblical-domain text
• Initialization for continued domain adaptation or supervised downstream fine-tuning
• Encoder hidden states for downstream task heads (classification, NER, etc.)

Training Pipeline

This release is the output of a two-stage pretraining pipeline.

Stage 1 — MLM pretraining from scratch (encoder)

• 24 epochs of masked language modeling at 256-token context
• 270,000 sequences from bible text, Christian books, biblical commentaries and synthetic data
• Final train loss 1.0679, train accuracy 76.42%

Stage 2 — Whole-word-masking continued pretraining (mlmcontinued) — this release

• 25 additional epochs of continued pretraining on top of Stage 1
• 18% whole-word-masking rate (whole-word, not single-piece)
• Final train loss 0.8958, train accuracy 79.66%

The MLM head was trained jointly with the body throughout both stages and is preserved in this release.

Evaluation

Evaluated on a 546-case domain-specific MLM benchmark covering bibliology, christology, ecclesiology, eschatology, hamartiology, pneumatology, soteriology, theology proper, and canonical knowledge. Full methodology and test case schema in EVAL.md.

Per-category highlights:

Comparison with bert-base-uncased

General-purpose BERT produces theologically incoherent completions on biblical text. Running google-bert/bert-base-uncased through the same 546-case eval shows the gap:

By difficulty — theo-bert-base on hard cases (94.2%) outperforms bert-base-uncased on easy cases (56.6%):

By category:

On contrastive theology — the most discriminative test type — bert-base-uncased is right 65% of the time but only confident (margin > 0.10) on 23% of cases. Theo-bert-base is right 98% of the time and confident on 91% of cases.

Residual failures cluster around Old Testament proper-noun recall (Jeremiah, Jonah, Job, Nebuchadnezzar) and multi-piece subword reconstruction (sabachthani, iniquity, Nebuchadnezzar). The benchmark suggests strong domain-specific MLM behavior on this suite; broader generalization beyond the eval distribution has not been independently verified.

Tokenizer

theo-bert-base uses the google-bert/bert-base-uncased tokenizer. The fast-tokenizer files (tokenizer.json, tokenizer_config.json) are bundled in this repo so AutoTokenizer.from_pretrained("toranb/theo-bert-base") and the Hub fill-mask widget work out of the box.

Tokenizer files are redistributed unmodified from google-bert/bert-base-uncased, released by Google under the Apache License 2.0.

Architecture

• 12 transformer blocks
• Hidden size 768
• 8 attention heads (head dim 96)
• Training sequence length 256 (rotary cache supports up to 2,560 tokens)
• Vocabulary size 30,522 via bert-base-uncased
• RoPE positional encoding applied to query and key projections
• RMS normalization on Q and K (no learnable gain)
• ReLU-squared MLP activation
• Gated value embeddings on even-indexed layers
• Learned residual interpolation between each block output and the initial token-embedding state
• MLM head: Linear → GELU → RMSNorm → Linear

Parameter count: 273,051,864 (≈273M).

Quick Start — Fill-Mask

from transformers import AutoModelForMaskedLM, AutoTokenizer

repo = "toranb/theo-bert-base"

tokenizer = AutoTokenizer.from_pretrained(repo)
model = AutoModelForMaskedLM.from_pretrained(repo, trust_remote_code=True)
model.eval()

inputs = tokenizer(
    "For God so loved the [MASK] that he gave his only Son.",
    return_tensors="pt",
)
outputs = model(**inputs)
mask_index = (inputs["input_ids"] == tokenizer.mask_token_id).nonzero(as_tuple=False)[0, 1]
top_ids = outputs.logits[0, mask_index].topk(5).indices.tolist()
print(tokenizer.convert_ids_to_tokens(top_ids))
# → ['world', 'universe', 'son', 'church', 'earth']

Quick Start — Encoder Hidden States

from transformers import AutoModel, AutoTokenizer

repo = "toranb/theo-bert-base"

tokenizer = AutoTokenizer.from_pretrained(repo)
model = AutoModel.from_pretrained(repo, trust_remote_code=True)
model.eval()

batch = tokenizer(
    ["faith working through love", "the kingdom of God"],
    padding=True, truncation=True, max_length=256, return_tensors="pt",
)
hidden = model(**batch).last_hidden_state  # [B, T, 768]
mask = batch["attention_mask"].unsqueeze(-1).float()
pooled = (hidden * mask).sum(1) / mask.sum(1).clamp(min=1)

Repository Contents

Scripts

Limitations

• Specialized for biblical and theological language; may underperform on broad general-domain NLP tasks.
• Tokenizer inherited from bert-base-uncased, so wordpiece behavior follows general English conventions rather than a theology-specific tokenizer.
• Trained at 256-token context. Longer inputs work within the rotary cache (up to 2,560 tokens), but extended-context behavior is not a primary target of this release.
• Training data is private, so external auditing of corpus composition is limited. The canonical-knowledge eval cases overlap by design with biblical text that appears in the training corpus, so the 88.4% recall on that category should be read as in-distribution recall, not held-out generalization.
• Encoder MLM — not an autoregressive decoder.

Release Details

• Exported from mlmcontinued/latest.pt (Stage 2 final epoch, training accuracy 79.66%)
• Source checkpoint loss 0.8958
• Released weights in fp16 for bandwidth efficiency (546 MB)
• Release format uses safetensors
• Loading requires trust_remote_code=True to register the custom architecture
• config.json declares torch_dtype: float32 so default loads upcast on read. Disk weights stay fp16 (small download); CPU inference is numerically safe by default. For GPU fp16 inference, pass dtype=torch.float16 to from_pretrained.