Comparing lean LLMs: GPT-5 Nano and Claude Haiku 4.5

OpenAI's GPT-5 Nano and Anthropic's Claude Haiku 4.5 represent a new generation of lightweight language models optimized for speed and cost rather than frontier performance. GPT-5 Nano excels in ultra-low latency tasks at roughly 20-25 times lower cost ($0.05 per million input tokens versus $1.00), while Claude Haiku 4.5 delivers stronger reasoning and coding capabilities despite higher pricing. Both models target real-time applications like chatbots and coding assistants, with different trade-offs between raw efficiency and analytical depth.