Tokenzier aside, a report shared on reddit found that the GPT 5.6 (edit: 5.5) series are incredibly thrifty with CoTs, resulting in cheaper bills than GLM 5.2 (let alone Opus/Fable): https://www.reddit.com/r/ZaiGLM/s/rUoG5adkPh

Chattiness remains an open issue for some of the SoTA open weights & (to a lesser extent) Claude.

That link does not mention 5.6.