I have first noticed logprob fluctuations in GPT-4o. Perhaps the same phenomenon is also going on with Turbo. I din‘t recall specifics but it was naming inconsistencies with variable names, meaning: same variable name got a typo somewhere, but the typo was close enough - perhaps a space vs. an underscore or something like that.

Model could be the same, but maybe some in the infra is different.

Is it the same? On the Models page of the API docs it says that GPT-4 is using the June 13th which would be different than the March 23rd.