The former. For the vast majority of verbs and situations I can think of, it is:
> [ te-form verb ]
> _I haven't [ past participle ] yet_
* _My hair hasn't dried yet_
* _I haven't read that book yet_
* _A song I haven't heard yet_
* * *
_I'm not [ present participle ] yet_ can be expressed with something like:
> [ verb stem ]
So for example, (literally _I haven't started eating yet_ ) is closer to _I'm not eating anything yet_.