Verdict: For coding agents, DeepSeek V4.1-Flash is the best open source LLM right now, because it lands level with Claude Opus 5 on software engineering while costing a fraction as much per million tokens. On DeepSeek's own release numbers it scores 74.2 on DeepSWE v1.1 against Claude Opus 5's 74.0 and GPT-5.6 Sol's 73.0, published on the model's release tracker entry . It loses badly on hard reasoning: 36.8 on Humanity's Last Exam without tools versus 56.3 for Claude Opus 5, per the same tabl...