A LoRA fine-tune of Qwen3.5-2B that translates a natural-language request plus a JSON sample into a jq program. The most accurate local backend in the nl2jq family — the jqgen --backend qwen-2b option. The LoRA adapter is merged; it loads as an ordinary model.

The 0.6B sibling remains the CLI's default; choose this backend when accuracy on everyday queries matters more than latency (~3–8s per query on laptop CPU; note T5-generalization is slightly lower than the 0.6B's — see the table).

Results

Execution accuracy on the frozen 400-item nl2jq-bench v1.0.0 (0% field overlap with training, novel domains, one-shot evaluation — see the bench card):

system	pass@1	valid	T1	T2	T3	T4	T5-gen
this model, greedy	0.46	0.75	0.67	0.61	0.47	0.33	0.13
this model + exec-rerank k=4 (the CLI config)	0.48	0.82	0.75	0.61	0.47	0.35	0.18
nl2jq-qwen3-0.6b-v6 (smaller sibling)	0.40	0.73	0.65	0.52	0.36	0.28	0.20
Claude Opus 4.8 (zero-shot, context row)	0.96	0.98	1.00	0.96	0.96	0.96	0.90

Read this as: reliable on elementary and core tasks over never-seen field names (T1 0.75 / T2 0.61 in the CLI configuration), progressively weaker on multi-stage compositions and exotic constructs. The frontier row is context, not a peer comparison. The exec-rerank config samples 4 candidates, repairs field references against the keys actually present in your JSON, and returns the first candidate that executes informatively — it is what jqgen runs by default.

Usage

cat data.json | jqgen --backend qwen-2b "total ridership per garage, highest first"

Or directly (non-thinking chat model — no reasoning-block handling needed):

python

from transformers import AutoModelForCausalLM, AutoTokenizer
tok = AutoTokenizer.from_pretrained("gauthierpiarrette/nl2jq-qwen3.5-2b")
model = AutoModelForCausalLM.from_pretrained("gauthierpiarrette/nl2jq-qwen3.5-2b")
msgs = [{"role": "system", "content": "You translate a natural-language request plus a "
         "sample of JSON into a single jq program. Output only the jq program, nothing else."},
        {"role": "user", "content": 'Request: highest fare\nJSON sample: [{"rider":"a","fare":12}]'}]
enc = tok.apply_chat_template(msgs, add_generation_prompt=True, return_tensors="pt",
                              enable_thinking=False)
ids = enc["input_ids"]
out = model.generate(ids, max_new_tokens=128,
                     eos_token_id=tok.convert_tokens_to_ids("<|im_end|>"))
print(tok.decode(out[0][ids.shape[1]:], skip_special_tokens=True).strip())

Training

LoRA (r=32, α=64, all-linear), 1 epoch over 150k execution-verified rows of the v7 synthetic data generation (per-example-unique field names built from real-text subword components, so copying — not recall — is the only strategy that works; plus generators for reduce/foreach/walk/paths/if and friends). All data is synthetic and execution-verified under jq 1.7.1; no scraped content; no frontier-model outputs. Development selection used a separate dev split — the frozen benchmark was evaluated exactly once.

Limitations

Multi-stage compositions (T4) and exotic constructs (T5) remain weak (0.35 / 0.18) — inspect the program before trusting output (the CLI prints it to stderr and supports --no-run).
~2–8s per query on laptop CPU via transformers; faster on any GPU / Apple Silicon.
jq 1.7.1 semantics; no modules/streaming.

License

Apache-2.0 (base model Apache-2.0; fine-tuned on CC BY 4.0 synthetic data).

GGUF / llama.cpp status

Not shipped, deliberately. A Q4_K_M conversion works mechanically (note: the base is a vision-language wrapper — a peft-merged text model must be re-wrapped with the base's vision tensors before convert_hf_to_gguf.py produces a loadable file), and the result loads without errors — but in our testing (llama.cpp b9957/b9964, CPU inference on macOS and Linux) generation for this hybrid GDN+MoE architecture never completed in reasonable time. We don't publish artifacts whose output we could not verify. Use the transformers path above; a GGUF will follow when llama.cpp's kernels for this architecture mature.

Code, benchmark tooling, and training pipeline: github.com/gauthierpiarrette/nl2jq