fine-tuned from scratch on Modal

SLM‑125M‑Instruct

A 125-million-parameter model, pretrained from random weights on legal and financial text, then fine-tuned to answer questions from a passage you give it. Paste a passage, ask about it, and it answers using only what's there.

125.8M
parameters
13,774
Q&A pairs
2.60
val perplexity
2
sft epochs
1,024
context
passage — the only thing it may use
your question about the passage
ready
The grounded answer will appear here.

What this is grounded Q&A

The base model only continues text — it can't answer questions. This is that base model after supervised fine-tuning on 13,774 teacher-generated, LLM-judged Q&A pairs, each grounded in a source passage. It now reads a passage and answers about it.

What it does well: extractive questions — who, what, where, which claims, what did the court hold, what does a clause require. It pulls the answer from the passage and phrases it directly.

Honest limits: at 125M it cannot do arithmetic (“6% of $50,000”, revenue growth) and has almost no world knowledge of its own — take away the passage and it has little to say. It answers from what you give it, not from memory.

chunk corpus → passages generate 2 Q&A / passage judge groundedness gate dedup semantic answer-only loss mask fine-tune 1×H100, 2 epochs

Passages drawn from US case law, SEC filings, and educational web text. First call may take ~10–20s while the model wakes from idle.

What it cost to build ~$27, end to end

The whole thing — a language model built from random weights to a working grounded-Q&A assistant — cost about the price of a large pizza. Every figure below is measured spend, not an estimate.

Pretraining
data pipeline + 8×H100, 4 epochs, 2.04B tokens + sampling
$14.43
SFT dataset
13,774 Q&A pairs — GPT‑5.4‑nano generates, GPT‑5.4‑mini judges, + pilots
$11.50
Fine-tuning
1×H100, 2 epochs kept, 3.9 minutes wall-clock
$0.21
Data pipeline compute
chunk / dedup / tokenize on Modal CPU
$0.60
Serving
scale-to-zero endpoint — $0 while idle
$0.00
Total ~$27

The output side dominated: at this scale, the teacher LLM writing and grading the training data ($11.50) cost nearly as much as pretraining the model itself ($14.43). Fine-tuning — the step everyone pictures as “the expensive part” — was 21 cents. The judge alone was 60% of the dataset bill, because verifying that an answer is truly grounded is harder than writing it.