DeepSeek is a leading Chinese AI research lab and LLM provider in 2026, offering frontier models like DeepSeek-V3 (general-purpose with Agent enhancements) and DeepSeek-R1 (reasoning-first, o1-level performance). It features massive context windows (128K+), exceptional coding/math/reasoning, free web/app chat access (no login for basics), and ultra-low-cost API (10-30x cheaper than competitors). Ideal for developers, researchers, enterprises, and everyday users seeking high-performance, affordable AI with open weights for many models.