SK Telecom released A.X 4.0 (pronounced "A dot X"), a large language model (LLM) optimized for Korean-language understanding and enterprise deployment, on July 03, 2025. Built on the open-source Qwen2.5 model, A.X 4.0 has been further trained with large-scale Korean datasets to deliver outstanding performance in real-world business environments.
Superior Korean Proficiency: Achieved a score of 78.3 on KMMLU, the leading benchmark for Korean-language evaluation and a Korean-specific adaptation of MMLU, outperforming GPT-4o (72.5).
Deep Cultural Understanding: Scored 83.5 on CLIcK, a benchmark for Korean cultural and contextual comprehension, surpassing GPT-4o (80.2).
Efficient Token Usage: A.X 4.0 uses approximately 33% fewer tokens than GPT-4o for the same Korean input, enabling more cost-effective and efficient processing.
Deployment Flexibility: Offered in both a 72B-parameter standard model (A.X 4.0) and a 7B lightweight version (A.X 4.0 Light).
Long Context Handling: Supports up to 131,072 tokens, allowing comprehension of lengthy documents and conversations. (Lightweight model supports up to 16,384 tokens length)
Performance
Model Performance
Benchmarks
A.X 4.0
Qwen3-235B-A22B (w/o reasoning)
Qwen2.5-72B
GPT-4o
Knowledge
KMMLU
78.32
73.64
66.44
72.51
CLIcK
83.51
74.55
72.59
80.22
KoBALT
47.30
41.57
37.00
44.00
MMLU
86.62
87.37
85.70
88.70
General
Ko-MT-Bench
86.69
88.00
82.69
88.44
MT-Bench
83.25
86.56
93.50
88.19
LiveBench2024.11
52.30
64.50
54.20
52.19
Instruction Following
Ko-IFEval
77.96
77.53
77.07
75.38
IFEval
86.05
85.77
86.54
83.86
Math
HRM8K
48.55
54.52
46.37
43.27
MATH
74.28
72.72
77.00
72.38
Code
HumanEval+
79.27
79.27
81.71
86.00
MBPP+
73.28
70.11
75.66
75.10
LiveCodeBench2024.10~2025.04
26.07
33.09
27.58
29.30
Long Context
LongBench<128K
56.70
49.40
45.60
47.50
Tool-use
FunctionChatBench
85.96
82.43
88.30
95.70
Lightweight Model Performance
Benchmarks
A.X 4.0 Light
Qwen3-8B (w/o reasoning)
Qwen2.5-7B
EXAONE-3.5-7.8B
Kanana-1.5-8B
Knowledge
KMMLU
64.15
63.53
49.56
53.76
48.28
CLIcK
68.05
62.71
60.56
64.30
61.30
KoBALT
30.29
26.57
21.57
21.71
23.14
MMLU
75.43
82.89
75.40
72.20
68.82
General
Ko-MT-Bench
79.50
64.06
61.31
81.06
76.30
MT-Bench
81.56
65.69
79.37
83.50
77.60
LiveBench
37.10
50.20
37.00
40.20
29.40
Instruction Following
Ko-IFEval
72.99
73.39
60.73
65.01
69.96
IFEval
84.68
85.38
76.73
82.61
80.11
Math
HRM8K
40.12
52.50
35.13
31.88
30.87
MATH
68.88
71.48
65.58
63.20
59.28
Code
HumanEval+
75.61
77.44
74.39
76.83
76.83
MBPP+
67.20
62.17
68.50
64.29
67.99
LiveCodeBench
18.03
23.93
16.62
17.98
16.52
🚀 Quickstart
with HuggingFace Transformers
transformers>=4.46.0 or the latest version is required to use skt/A.X-4.0-Light
pip install transformers>=4.46.0
Example Usage
importtorchfromtransformersimportAutoModelForCausalLM,AutoTokenizermodel_name="skt/A.X-4.0-Light"model=AutoModelForCausalLM.from_pretrained(model_name,torch_dtype=torch.bfloat16,device_map="auto",)model.eval()tokenizer=AutoTokenizer.from_pretrained(model_name)messages=[{"role":"system","content":"당신은 사용자가 제공하는 영어 문장들을 한국어로 번역하는 AI 전문가입니다."},{"role":"user","content":"The first human went into space and orbited the Earth on April 12, 1961."},]input_ids=tokenizer.apply_chat_template(messages,add_generation_prompt=True,return_tensors="pt").to(model.device)withtorch.no_grad():output=model.generate(input_ids,max_new_tokens=128,do_sample=False,)len_input_prompt=len(input_ids[0])response=tokenizer.decode(output[0][len_input_prompt:],skip_special_tokens=True)print(response)# Output:# 1961년 4월 12일, 최초의 인간이 우주로 나가 지구를 공전했습니다.
with vLLM
vllm>=v0.6.4.post1 or the latest version is required to use tool-use function
pip install vllm>=v0.6.4.post1
# if you don't want to activate tool-use function, just commenting out below vLLM optionVLLM_OPTION="--enable-auto-tool-choice --tool-call-parser hermes"
vllm serve skt/A.X-4.0-Light $VLLM_OPTION
Example Usage
fromopenaiimportOpenAIdefcall(messages,model):completion=client.chat.completions.create(model=model,messages=messages,)print(completion.choices[0].message)client=OpenAI(base_url="http://localhost:8000/v1",api_key="api_key")model="skt/A.X-4.0-Light"messages=[{"role":"user","content":"에어컨 여름철 적정 온도는? 한줄로 답변해줘"}]call(messages,model)# Output:# ChatCompletionMessage(content='여름철 적정 에어컨 온도는 일반적으로 24-26도입니다.', refusal=None, role='assistant', audio=None, function_call=None, tool_calls=[], reasoning_content=None)messages=[{"role":"user","content":"What is the appropriate temperature for air conditioning in summer? Response in a single sentence."}]call(messages,model)# Output:# ChatCompletionMessage(content='The appropriate temperature for air conditioning in summer generally ranges from 72°F to 78°F (22°C to 26°C) for comfort and energy efficiency.', refusal=None, role='assistant', audio=None, function_call=None, tool_calls=[], reasoning_content=None)
Examples for tool-use
fromopenaiimportOpenAIdefcall(messages,model):completion=client.chat.completions.create(model=model,messages=messages,tools=tools)print(completion.choices[0].message)client=OpenAI(base_url="http://localhost:8000/v1",api_key="api_key")model="skt/A.X-4.0-Light"calculate_discount={"type":"function","function":{"name":"calculate_discount","description":"원가격과 할인율(퍼센트 단위)을 입력받아 할인된 가격을계산한다.","parameters":{"type":"object","properties":{"original_price":{"type":"number","description":"상품의 원래 가격"},"discount_percentage":{"type":"number","description":"적용할 할인율(예: 20% 할인의 경우 20을 입력)"}},"required":["original_price","discount_percentage"]}}}get_exchange_rate={"type":"function","function":{"name":"get_exchange_rate","description":"두 통화 간의 환율을 가져온다.","parameters":{"type":"object","properties":{"base_currency":{"type":"string","description":"The currency to convert from."},"target_currency":{"type":"string","description":"The currency to convert to."}},"required":["base_currency","target_currency"]}}}tools=[calculate_discount,get_exchange_rate]### Slot filling ###messages=[{"role":"user","content":"우리가 뭘 사야되는데 원래 57600원인데 직원할인 받을 수 있거든? 할인가좀 계산해줘"}]call(messages,model)# Output:# ChatCompletionMessage(content='할인율을 알려주시겠습니까?', refusal=None, role='assistant', audio=None, function_call=None, tool_calls=[], reasoning_content=None)### Function calling ###messages=[{"role":"user","content":"우리가 뭘 사야되는데 원래 57600원인데 직원할인 받을 수 있거든? 할인가좀 계산해줘"},{"role":"assistant","content":"할인율을 알려주시겠습니까?"},{"role":"user","content":"15% 할인 받을 수 있어."},]call(messages,model)# Output: # ChatCompletionMessage(content=None, refusal=None, role='assistant', audio=None, function_call=None, tool_calls=[ChatCompletionMessageToolCall(id='chatcmpl-tool-7778d1d9fca94bf2acbb44c79359502c', function=Function(arguments='{"original_price": 57600, "discount_percentage": 15}', name='calculate_discount'), type='function')], reasoning_content=None)### Completion ###messages=[{"role":"user","content":"우리가 뭘 사야되는데 원래 57600원인데 직원할인 받을 수 있거든? 할인가좀 계산해줘"},{"role":"assistant","content":"할인율을 알려주시겠습니까?"},{"role":"user","content":"15% 할인 받을 수 있어."},{"role":"tool","tool_call_id":"random_id","name":"calculate_discount","content":"{\"original_price\": 57600, \"discount_percentage\": 15, \"discounted_price\": 48960.0}"}]call(messages,model)# Output: # ChatCompletionMessage(content='57600원의 상품에서 15% 할인을 적용하면, 할인된 가격은 48960원입니다.', refusal=None, role='assistant', audio=None, function_call=None, tool_calls=[], reasoning_content=None)
License
The A.X 4.0 Light models are licensed under Apache License 2.0.
Citation
@article{SKTAdotX4Light,
title={A.X 4.0 Light},
author={SKT AI Model Lab},
year={2025},
url={https://huggingface.co/skt/A.X-4.0-Light}
}