Not sure if GLM-4.5 Air is good, but non-Air one is fabulous. I know for free API access there is pollinations ai project. Also llm7. If you just use the web chat's you can use most of the best models for free without API. There are ways to 'emulate' an API automatically.. I was thinking about adding this to my aicodeprep-gui app so it could automatically paste and then cut. Some MCP servers exist that you can use and it will automatically paste or cut from those web chat's and route it to an API interface.
OpenAI offers free tokens for most models, 2.5mil or 250k depending on model. Cerebras has some free limits, Gemini... Meta has plentiful free API for Llama 4 because.. lets face it, it sucks, but it is okay/not bad for stuff like summarizing text.
If you really wanted to code for exactly $0 you could use pollinations ai, in Cline extension (for VS Code) set to use "openai-large" (which is GPT 4.1). If you plan using all the best web chat's like Kimi K2, z.ai's GLM models, Qwen 3 chat, Gemini in AI Studio, OpenAI playground with o3 or o4-mini. You can go forever without being charged money. Pollinations 'openai-large' works fine in Cline as an agent to edit files for you etc.