laya-code

A code-relevance re-ranker fine-tuned from Laya (ModernBERT-large encoder + typed-decision head, 421M parameters). Given a task description and a source-code chunk, it answers one yes/no (noul) question with a calibrated probability:

question: Is this source code relevant to the software change: "{task}"?
state:    file: <path> (lines a-b)\n<code>        (truncated to 128 tokens in production)

It is the default re-ranker of laya-codex, which feeds Claude Code the most relevant code spans for a prompt (tree-sitter chunks, then Moon BM25 candidates, then laya-code re-ranking).

Model details

Training data

Weak supervision from git history. Nothing was hand-labelled.

• 8 training repositories (mixed Rust, Python, TypeScript and JavaScript): openai/codex, TinDang97/velos, MervinPraison/PraisonAI, badlogic/pi-mono, Portkey-AI/gateway (local ai-guard checkout), TinDang97/python-dependency-injector, Netflix/dispatch and pilotspace/hydroa (local ai-proxy checkout). Source: finetune/repos.py.

• Held out (never used for training or calibration): pilotspace/moon and pilot-space. Moon client codebases (helios, helios-mono, lunaris) were left out so that Moon vocabulary does not leak into the Moon eval. A root-commit check rejects forks and clones of each other and of the held-out repos.

• Examples: up to 600 non-merge commits per repo (the build_data.py default) that touch 1–4 source files and have an informative subject (at least 20 characters). The task is the subject plus a short first body line. The candidate list is the BM25 top 12 over other files plus the parent-revision windows of the touched files (40-line windows, stride 30). Labels: 1.0 for a window that overlaps a changed hunk, 0.7 for another window of a touched file, 0 for other files. Extra examples: hunks BM25 missed (label 1.0), a random same-file window (label 0.4) and random windows from other files (label 0).

• Size: 50,926 pairs, split by commit hash into 45,790 train and 5,136 validation pairs. Train pairs: 2,779 candidate positives, 5,609 candidate same-file, 24,768 candidate negatives, 4,656 extra positives, 2,392 same-file, 5,586 random negatives. Per-repo counts (v2 data; the warm start used v1 data from the same repos):

  repo	train commits	val commits	train pairs	val pairs
  PraisonAI	231	18	3,711	280
  ai-guard	460	40	7,404	665
  ai-proxy	200	23	3,293	380
  codex	446	54	7,676	932
  dispatch	447	53	7,347	863
  pi-mono	439	61	7,386	1,013
  python-dependency-injector	453	47	7,066	744
  velos	117	16	1,907	259

• Training: top 8 of 28 encoder layers, the final norm and the decision head. fp32 on an M4 Pro (MPS). AdamW; learning rate 2e-5 for the encoder and 1e-4 for the head. 32 sequences per update. Log loss against soft targets. 536 updates on v2 data, warm-started from 300 updates on v1 data (about 2.3 h in total). Checkpoint chosen by lowest validation NLL. The noul:2 temperature was then refitted on the validation split, using the exported F16 weights.

Evaluation

All numbers come from files in the laya-codex repository and are quoted as recorded. Gold labels are file-level: the files the commit touched. Candidates are BM25 windows at HEAD.

Re-ranker comparison, 128-token state (production setting)

spike/results/compare_models.json (spike/compare_models.py): the 40 most recent qualifying moon commits, BM25 top 24, state truncated to 128 tokens, probabilities pooled over all candidates (base rate 0.309).

Held-out evaluation, 256-token state (training protocol)

spike/results/finetune_eval.json (finetune/eval.py): 40 tasks per held-out repo, BM25 top 32, state truncated to 256 tokens. Paired bootstrap over the tasks.

Under this protocol, laya-code clearly improves calibration and discrimination. It puts more gold-file spans in the top 10: RRF P@10 rose by +0.055 (95% CI [0.013, 0.098]) on moon and by +0.070 ([0.033, 0.108]) on pilot-space. Its RRF MRR did not beat laya-base's: −0.066 ([−0.195, 0.061]) on moon and −0.049 ([−0.172, 0.073]) on pilot-space. For that reason, laya-codex fuses laya-code by score ((1−w)·lexical + w·P, w = 0.5) rather than by RRF.

End to end, the laya-codex paired Claude Code benchmark (20 moon tasks, docs/RESULTS.md) measured −45% code-reading tokens and −25% wall-clock time for the whole pipeline, with no loss of answer recall. The same document reports that the model's marginal contribution over lexical-only ranking is within run-to-run noise at n = 20. Do not read the pipeline numbers as a property of this model.

Intended use

• Re-ranking lexical (BM25) candidates of source-code chunks for a natural-language software-change task, as a calibrated P(relevant).
• Gating or fusing retrieval results by probability; P is calibrated to the training distribution (ECE ≤ 0.06 on held-out repos).

Out of scope and limitations

• Weak labels. A commit touching a file does not make every window of it relevant, and the file-level gold is coarse.
• Small evaluation. Each held-out set has 40 tasks, and most CIs are wide. The two protocols (128 vs 256 tokens, top 24 vs 32) give different absolute numbers, as shown above.
• Low probabilities. P rarely exceeds 0.5 (max 0.49 on moon, 0.50 on pilot-space at 256 tokens). Use rank or score fusion, or a threshold near 0.4, not "P ≥ 0.5 means relevant".
• Under-trained. Only about half an epoch of the v2 data was used, on a shared laptop. Validation AUROC was still rising when training stopped.
• English prompts only. Training covered Rust, Python, TypeScript and JavaScript; other languages are untested.
• Other tasks untested. It is not a general Laya replacement: choice/score questions (for example, task scope) were not trained, and zero-shot scope accuracy is poor (spike/results/scope_eval.json).
• Too slow for interactive CPU use. At 421M parameters, CPU re-ranking of 24 candidates is too slow for interactive use. laya-codex runs it on Metal, or falls back to lexical ranking.
• Legal status of training data. The model was trained on permissively licensed public code plus the author's own repositories. It is a classifier and cannot reproduce that code, but the legal status of weights trained on source code is not settled.

License and attribution

Apache-2.0, like the base model. laya-code is a Derivative Work of convaiinnovations/laya (Apache-2.0, © Convai Innovations), which builds on answerdotai/ModernBERT-large (Apache-2.0). The modified files are model.safetensors and rl_agent_config.json; every other file is unchanged from the base. See NOTICE.

Files

See MANIFEST.sha256 for the sha256 of every uploaded file.