For agentic coding I found the price difference more modest due to prompt caching, which most GLM providers on Openrouter don't offer, but Anthropic does. Look at the cache read/write columns: https://openrouter.ai/z-ai/glm-4.5
Been playing with Grok Code Fast 1 in Cline via Open Router. It supports prompt caching as far as I can tell, and it certainly is cheap. It's been quite good for the stuff I've tried. YMMV.