What does "blended $0.30 per 1M tokens" mean? Is that input or output or average across the two? (asking as am trying to benchmark that cost against public GLM providers on Openrouter)

It's an average across the two.

One would still have to guess what the ratio of input tokens to output tokens is. (I would say 10:1 off the cuff, assuming this is editing an existing codebase)