A.X LLM Series

SK Telecom’s proprietary Korean-specialized large language models

A.X LLM

A.X LLM is a series of Korean-specialized large language models independently developed by SK Telecom. A.X K2, A.X K1, A.X 4.0, and A.X 3.1 are publicly available as open source and can be freely used for academic research and commercial purposes.

Project Information

Developer: SK Telecom
License: Apache-2.0
GitHub:
Hugging Face:

Key Features

A.X K2 Series

688B-A33B Sparse MoE: A large-scale Mixture-of-Experts model with 688B total parameters and 33B active parameters per token
Mathematical and scientific reasoning: Scored 29/42 on IMO 2026, reaching the gold-medal threshold, and tied for the top score on the MathArena AIME 2026 leaderboard with 97.1%
Sparse Gated Attention (SGA): Selects the most relevant information in long contexts to improve accuracy and inference efficiency
Long-context support: Supports a 262,144-token (256K) context length
Native FP8 training and FP8 checkpoint: Enables efficient FP8 serving without a separate post-hoc quantization step
Deployment checkpoints: Provides GGUF and NVFP4 quantized builds together with EAGLE3 and DSpark draft models for faster inference
Multimodal derivative lineup: Also publishes model cards and technical materials for A.X VE, a vision encoder trained from scratch, and A.X K2 ALM, an audio language model for speech understanding and generation

A.X K1 Series

519B-A33B Sparse MoE: A large-scale Mixture-of-Experts model with 519B total parameters and 33B active parameters per token
Hybrid Reasoning Control: Think / Non-Think modes allow users to choose between deeper reasoning and lower latency
Long-context support: Supports a 131,072-token context length
Multilingual and code tokenizer: BBPE-based tokenizer optimized for Korean, English, Chinese, Japanese, Spanish, and code data

A.X 4.0 Series

72B model: Optimized for large-scale Korean language processing
7B Light Model: Efficient lightweight model
Korean token efficiency: ~33% improvement over GPT-4o
Real-world deployment: Used in SK Telecom’s A. call summary service

A.X 3.1 Series

34B model: Independently developed sovereign AI model
Light Model: Lightweight version
Significantly enhanced coding and mathematical reasoning capabilities
KMMLU benchmark: 69.20 points (~88% of A.X 4.0 performance)

A.X 4.0-VL-Light

Vision-Language model: Integrated image and text processing
Multimodal AI: Capable of understanding and analyzing visual information

Technical Achievements

Korean Language Processing Capabilities

Excellent performance on KMMLU (Korean Massive Multitask Language Understanding)
Specialized in Korean conversation, document understanding, and summarization
Optimized for Korean business environments

Model Architecture

A.X K2: A from-scratch 688B-A33B proprietary Sparse MoE model
A.X K1: A from-scratch 519B-A33B proprietary Sparse MoE model
A.X 3 series: Sovereign AI developed from scratch
A.X 4 series: Open-source models enhanced with CPT (Continual Pre-Training) using large-scale Korean data

Use Cases

SK Telecom Internal Services

A. call summary service (since May 2025)
Customer service chatbots
Internal document analysis and search

Potential Applications

Korean conversational AI services
Text generation and summarization
Translation and sentiment analysis
Code generation and mathematical problem solving
Korean content creation

Benchmark Performance

Model	Parameters	Representative Score	Features
A.X K2	688B-A33B	IMO 2026 29/42 (gold-medal threshold) / AIME 2026 97.1	SGA, 256K context
A.X K1	519B-A33B	KMMLU 80.2 (Thinking Mode)	Sparse MoE, long context
A.X 4.0	72B	KMMLU 78.3	High performance
A.X 3.1	34B	KMMLU 69.2	Independently developed
A.X 4.0 Light	7B	-	Efficiency
A.X 3.1 Light	-	-	Lightweight