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CodeLanguage-Qwen3.5-2B-v8

Merged full model (base Qwen/Qwen3.5-2B + LoRA adapter, merged via peft.merge_and_unload()) that identifies which programming languages are embedded in a user prompt across 25 languages and configuration formats. This is a self-contained checkpoint — load it directly (no PEFT step) and serve it on vLLM (v0.21.0+). Trained on a combined dataset of Rosetta Code snippets and curated config-language samples (Dockerfile, YAML, Terraform, Makefile, SQL). The model is fine-tuned to emit a strict JSON object describing the languages found:

{"is_valid": true, "category": {"Python": true, "Bash": true}}

is_valid is true when at least one code/config snippet is present and false for natural-language-only prompts. category contains only the detected languages, each mapped to true; if no code is present category is {}.

Quick start

Text-only model. The base Qwen/Qwen3.5-2B declares the multimodal Qwen3_5ForConditionalGeneration architecture (it carries a vision tower in its weights), but this is a text-in / text-out language guard — it never consumes images and only emits the JSON verdict. Send only text prompts; vLLM auto-detects text-only mode and prints All limits of multimodal modalities ... set to 0, running in text-only mode at startup. (language_model_only=True would in theory skip loading the vision-tower weights, but on vLLM v0.21.0 it crashes Qwen3_5ForCausalLM.__init__ with a vision_config attribute error — leave it off until a later vLLM release fixes that path.)

vLLM (recommended — needs vLLM >= 0.21.0 for the Qwen3.5/Mamba runner)

from vllm import LLM, SamplingParams
from transformers import AutoTokenizer
import json, re

MODEL = "Accuknoxtechnologies/CodeLanguage-Qwen3.5-2B-v8"
SYSTEM_MSG = """You are a code language identifier. For the given user prompt, decide whether it contains any embedded source code (program source or recognizable code-like configuration). Output exactly one JSON object and nothing else: {"is_valid": <true|false>, "category": {"<Lang>": true, ...}}.
No preamble. No explanation. No <think> tags. No markdown code fences. No trailing prose.
Rules:
  - is_valid is TRUE when the prompt contains at least one code/config snippet, FALSE when the prompt is plain natural-language only.
  - category contains ONLY the languages that appear, each mapped to true. If no code is present, category is the empty object {}.
  - When multiple languages appear, list every distinct one (still only true).
Allowed language keys (use these exact spellings):
  Python, JavaScript, Java, C, C++, C#, Go, Rust, Kotlin, Swift, Ruby, R, Scala, Perl, Lua, Bash, PowerShell, Batch, SQL, Dockerfile, YAML, Makefile, Terraform, AWK, jq"""

llm = LLM(
    model=MODEL,
    trust_remote_code=True,
    dtype="bfloat16",
    max_model_len=4096,
    # vLLM auto-detects text-only when no multimodal inputs are sent.
    # Do NOT pass language_model_only=True here — see the note above.
)
tokenizer = AutoTokenizer.from_pretrained(MODEL, trust_remote_code=True)
sampling = SamplingParams(temperature=0.0, max_tokens=220, stop=["\n\n\n"])

def langid(prompt: str) -> dict:
    chat = tokenizer.apply_chat_template(
        [{"role":"system","content":SYSTEM_MSG},
         {"role":"user","content":prompt}],
        tokenize=False, add_generation_prompt=True, enable_thinking=False)
    out = llm.generate([chat], sampling)
    text = out[0].outputs[0].text
    return json.loads(re.search(r'\{.*\}', text, re.DOTALL).group(0))

Plain transformers

from transformers import AutoModelForCausalLM, AutoTokenizer
import torch, json, re

MODEL = "Accuknoxtechnologies/CodeLanguage-Qwen3.5-2B-v8"
SYSTEM_MSG = """You are a code language identifier. For the given user prompt, decide whether it contains any embedded source code (program source or recognizable code-like configuration). Output exactly one JSON object and nothing else: {"is_valid": <true|false>, "category": {"<Lang>": true, ...}}.
No preamble. No explanation. No <think> tags. No markdown code fences. No trailing prose.
Rules:
  - is_valid is TRUE when the prompt contains at least one code/config snippet, FALSE when the prompt is plain natural-language only.
  - category contains ONLY the languages that appear, each mapped to true. If no code is present, category is the empty object {}.
  - When multiple languages appear, list every distinct one (still only true).
Allowed language keys (use these exact spellings):
  Python, JavaScript, Java, C, C++, C#, Go, Rust, Kotlin, Swift, Ruby, R, Scala, Perl, Lua, Bash, PowerShell, Batch, SQL, Dockerfile, YAML, Makefile, Terraform, AWK, jq"""

tokenizer = AutoTokenizer.from_pretrained(MODEL, trust_remote_code=True)
model = AutoModelForCausalLM.from_pretrained(
    MODEL, torch_dtype=torch.bfloat16, device_map="auto", trust_remote_code=True,
).eval()

def langid(prompt: str) -> dict:
    chat = tokenizer.apply_chat_template(
        [{"role":"system","content":SYSTEM_MSG},
         {"role":"user","content":prompt}],
        tokenize=False, add_generation_prompt=True, enable_thinking=False)
    inputs = tokenizer(chat, return_tensors="pt").to(model.device)
    out = model.generate(**inputs, max_new_tokens=220, do_sample=False)
    text = tokenizer.decode(out[0, inputs["input_ids"].shape[1]:], skip_special_tokens=True)
    return json.loads(re.search(r'\{.*\}', text, re.DOTALL).group(0))

System prompt

The model was trained with the exact system prompt below. Pass it verbatim at inference time — the output schema depends on this prompt.

You are a code language identifier. For the given user prompt, decide whether it contains any embedded source code (program source or recognizable code-like configuration). Output exactly one JSON object and nothing else: {"is_valid": <true|false>, "category": {"<Lang>": true, ...}}.
No preamble. No explanation. No <think> tags. No markdown code fences. No trailing prose.
Rules:
  - is_valid is TRUE when the prompt contains at least one code/config snippet, FALSE when the prompt is plain natural-language only.
  - category contains ONLY the languages that appear, each mapped to true. If no code is present, category is the empty object {}.
  - When multiple languages appear, list every distinct one (still only true).
Allowed language keys (use these exact spellings):
  Python, JavaScript, Java, C, C++, C#, Go, Rust, Kotlin, Swift, Ruby, R, Scala, Perl, Lua, Bash, PowerShell, Batch, SQL, Dockerfile, YAML, Makefile, Terraform, AWK, jq

Evaluation (transformers)

Evaluated on 200 held-out prompts drawn from test_dataset_langid.csv (same single + multi + benign composition as training).

  • Evaluation timestamp: 2026-05-24 12:53 UTC
  • GPU: NVIDIA A10G
  • Source adapter: Accuknoxtechnologies/CodeLanguage-Qwen3.5-2B-v8
  • JSON parse errors: 0/200 (0.0%)

Top-level metrics

Metric Value
is_valid accuracy 1.0000
Language-set exact match 0.9650
Binary F1 (positive = contains code) 1.0000
Binary precision 1.0000
Binary recall 1.0000
Macro F1 across languages 0.9701

Confusion matrix — binary is_valid decision

Positive class = the prompt contains code (is_valid=True).

predicted contains-code predicted no-code
actual contains-code TP = 181 FN = 0
actual no-code FP = 0 TN = 19

Per-language metrics

Only languages that appear in either the actual or predicted labels are listed.

Language support precision recall F1
Python 14 1.000 1.000 1.000
Terraform 14 1.000 1.000 1.000
Java 12 1.000 0.917 0.957
C 12 0.857 1.000 0.923
Rust 12 1.000 1.000 1.000
AWK 12 1.000 0.917 0.957
Ruby 11 1.000 1.000 1.000
R 11 0.846 1.000 0.917
Go 10 1.000 1.000 1.000
Swift 10 1.000 1.000 1.000
Scala 10 1.000 0.800 0.889
SQL 10 1.000 1.000 1.000
jq 10 0.909 1.000 0.952
JavaScript 9 0.900 1.000 0.947
Kotlin 9 1.000 1.000 1.000
Perl 9 1.000 1.000 1.000
PowerShell 9 1.000 1.000 1.000
Batch 9 1.000 1.000 1.000
YAML 9 1.000 0.889 0.941
C++ 7 1.000 0.857 0.923
C# 7 1.000 1.000 1.000
Lua 7 1.000 0.857 0.923
Bash 7 1.000 1.000 1.000
Dockerfile 6 0.857 1.000 0.923
Makefile 6 1.000 1.000 1.000

Inference latency

  • Mean: 0.99 s/prompt
  • Median: 0.94 s/prompt
  • p95: 1.34 s/prompt
  • Max: 1.64 s/prompt

Training setup

  • Base model: Qwen/Qwen3.5-2B (loaded in full precision (bf16 / fp16, no bitsandbytes quantization))
  • LoRA: r=16, alpha=32, dropout=0.05, target modules = {q,k,v,o,gate,up,down}_proj
  • Optimizer: adamw_torch, lr=1e-4, cosine schedule, warmup 5%
  • Epochs: 3
  • Precision: bf16 if available, else fp16
  • Effective batch size: 8 (per-device 1 + grad-accum 8), gradient checkpointing on
  • Max sequence length: 3200 tokens
  • Training data: 10,000 rows (7,000 single-language + 2,000 multi-language + 1,000 benign)
  • Languages: 25 (programming + config formats)

Supported languages

The model emits one or more of these keys in the category map of its JSON output:

Python, JavaScript, Java, C, C++, C#, Go, Rust, Kotlin, Swift, Ruby, R, Scala, Perl, Lua, Bash, PowerShell, Batch, SQL, Dockerfile, YAML, Makefile, Terraform, AWK, jq

Evaluation — vLLM serving (merged model, text-only)

Same 500 held-out prompts, served through vLLM 0.21.0's native Qwen3.5/Mamba runner instead of the transformers .generate() loop above. Only text prompts are sent; vLLM auto-detects text-only mode. This reflects production serving accuracy + latency.

  • Engine: vLLM 0.21.0, text-only (auto (limit_mm_per_prompt=0)), dtype bf16, greedy decoding
  • GPU: NVIDIA A10G
  • JSON parse errors: 0/500 (0.0%)

Accuracy (vLLM)

Metric Value
is_valid accuracy 1.0000
Language-set exact match 0.9700
Binary F1 (positive = contains code) 1.0000
Binary precision 1.0000
Binary recall 1.0000
Macro F1 across languages 0.9771

Confusion matrix — binary is_valid (vLLM)

predicted contains-code predicted no-code
actual contains-code TP = 450 FN = 0
actual no-code FP = 0 TN = 50

vLLM inference latency (single-stream, batch = 1)

Stat ms / prompt
Mean 200.0
Median 186.2
p95 278.9
p99 343.7
Max 1990.9
Under 1 s 99.6%

vLLM throughput (single batched submit, continuous batching)

  • Prompts/sec: 18.12
  • Output tokens/sec: 260.7
  • Input tokens/sec: 15441.4
  • Batched wall time for all 500 prompts: 27.60 s

Model card generated automatically by eval_and_push_card.py on 2026-05-24 12:53 UTC.

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Evaluation results

  • is_valid accuracy on LangID Guard Held-out Test Set
    self-reported
    1.000
  • language-set exact match on LangID Guard Held-out Test Set
    self-reported
    0.965
  • binary F1 (positive=contains code) on LangID Guard Held-out Test Set
    self-reported
    1.000
  • macro F1 over languages on LangID Guard Held-out Test Set
    self-reported
    0.970
  • binary precision (positive=contains code) on LangID Guard Held-out Test Set
    self-reported
    1.000
  • binary recall (positive=contains code) on LangID Guard Held-out Test Set
    self-reported
    1.000