DeepSeek V4: New Open-Weights Models with 1M Token Context at Low Cost

ArticleSimon WillisonNews

DeepSeek has introduced DeepSeek-V4-Pro and DeepSeek-V4-Flash under an MIT licence. Simon Willison reviews their Mixture of Experts architecture, KV cache efficiency gains, and pricing compared to OpenAI, Google, and Anthropic.

Key points

  1. DeepSeek-V4-Pro features 1.6T total parameters (49B active), making it the largest open-weights model to date.
  2. DeepSeek-V4-Flash has 284B total parameters (13B active); both models feature a 1-million-token context window under the MIT licence.
  3. API pricing is set at $0.14 input / $0.28 output per million tokens for Flash, and $1.74 input / $3.48 output for Pro.
  4. Substantial efficiency improvements: At 1M context, Pro requires 27% of single-token FLOPs and 10% of the KV cache size compared to DeepSeek-V3.2.
  5. Self-reported benchmarks place the architecture roughly 3 to 6 months behind current frontier models like GPT-5.4 and Gemini 3.1 Pro.

Why it matters

DeepSeek continues to disrupt the frontier AI market by coupling open weights with aggressive pricing. Lower FLOP requirements and reduced KV-cache demands at 1M tokens make frontier-calibre MoE architectures much more accessible for self-hosting and cost-constrained deployments.

Analysis

The V4 series demonstrates that architectural optimisation in Mixture-of-Experts routing and memory management can substantially cut API costs. As Willison shows in his price comparison, DeepSeek undercut offerings like GPT-5.4 Nano and Claude Sonnet 4.6 significantly. Although DeepSeek admits trailing the frontier by several months, their open MIT licensing and efficiency gains challenge proprietary closed-model pricing models.

Found in

Summary generated by AI (Gemini 3.8 Flash, 27 September 2026). It may contain errors – the original source is authoritative.

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