In a note to investors, included in VentureBeat's report, Cohen pointed out that previous marketing budgets have predicted the releases of other big releases from Take-Two Interactive, including Red Dead Redemption 2. This led industry analyst Jeff Cohen to predict that this spike is because GTA 6 is expected to release within this period (which now looks likely). As reported by VentureBeat, Take-Two's 10-K SEC filing from 2020 (which lays out financial plans for the next five years) shows that the company expects to spend $89 million on marketing between April 2023, and the end of March 2024 - that's a huge spike and, as the report points out, more than half the marketing budget expected for any other fiscal year over the next decade However, while the Kotaku report didn't give us an idea of when GTA 6 will release, publisher Take-Two Interactive's marketing budget may have given us our most solid GTA 6 release date hint. So, the game may be further along in development than we expected.
Kotaku's report claimed this new installment is planned to be a "moderately sized release" (so, probably still pretty big) which will be "expanded with regular updates over time".
Rockstar Games has confirmed that GTA 6 is in "active development" and, according to a Kotaku report, this "new entry in the Grand Theft Auto series" was in early development as of April 2020.