Chidbhananda (an advaitin monk) in his Gita translation explained Sat & Asat. He explains that when Krishna told Arjuna that He's both sat & asat, Krishna was referring to saguna brahman.
Chidbhananda explains -
Sat = being / vyakta / material manifestation.
Asat = non-being / avyakta / non-manifestation / subtlety.
And both sat & asat are part of Prakriti / Maya / SagunaBrahman, since sat and asat are a type of qualities or features that can be applied to only Saguna Brahm and not to Nirguna Brahm ... Nirguna Brahm on the other hand is beyond "sat/vyakta" and "asat/avyakta" features. Here is the link to the ebook. Ch13,v12, page 89 & 90 Chidbhananda Gita The pages are all in a scrabled order in this ebook. After page 89 , page 94 appears. You need to flip a few pages back to get to pg.90
On the other hand, in Chandogya upanishad, chapter 6, Section 2, verses 1 & 2, Sage Aruni aka Uddalaka describes Brahman (nirguna) as Sat. Here are the verses-
Verse 1 ... Sat – Being (‘is-ness’), eva – only, saumya – dear boy, idam – this, agra – in the beginning, asid (aasith) – was, ekam – one, eva – only, advitiyam – without a second (non-dual), tad – about that, haika (aika) – some, ahuh – say, asad (asath) – non-being (void), eva – only, idam – this, agra – in the beginning, asid (aasith) – was, ekam – one, eva – only, advitiyam – without a second (non-dual), tasmad asatah (asathah) – from that non-being, saj (sath) – being (“is-ness”), jayata – arose/was born
In the beginning, dear boy, this was Being alone, one only, without a second. Some say that, in the beginning, this was Non-being alone, one only, without a second. From that Non-being arose Being.
Verse 2 ... Kutah – whence/how, tu – but, khalu – indeed, saumya – dear boy, evam – so, syat – could it be, iti hovaca – so (Aruni) said, katham – how, asatah (asathah) – from Non-being (Void), saj (sath) – Being (“is-ness”), jayet – could arise, iti – so (he said), sat (sath) – Being (“is-ness”), tu – in truth, eva – only, saumya – dear boy, idam – this, agra – in the beginning, asid (aasith) – was, ekam – one, eva – only, advitiyam – without a second (non-dual)
Aruni (Uddalaka) said, ‘But how, indeed, dear boy, could it be so? How could Being arise from Non-being? In truth, dear boy, in the beginning (before creation), there was Being alone, one only, without a second.
I'm a little confused here. Does sat simply means existence or being as Aruni describes, which Aruni ascribes it to Nirguna Brahman ... or is Chidbhananda's explanation correct, that sat(vyakta) & asat(avyakta) are features of Saguna Brahman and that the term 'sat' is not ANY KIND of existence but only material manifestation or vyaktaroopa?