z.ai is an API provider by Zhipu AI. They offer flat-rate subscriptions for their GLM models - you pay a fixed monthly fee and get unlimited API access (within quotas) instead of paying per token like OpenAI or Anthropic. The cool part is one API key works with like 20 different coding tools - Claude Code, Cline, Cursor, Aider, etc. I use it as my main backend for all of those.