Not just a threshold — a cliff
Straight from the statute: no credit shall be allowed to the estate of any decedent whose New York taxable estate exceeds one hundred five percent of the basic exclusion amount. Below the exclusion, a full credit cancels the tax. Between 100% and 105% of the exclusion, the credit phases out on a sliding scale. Above 105%, there's no credit at all — the graduated rate table applies to the entire estate, not just the amount over the exemption.
A $150,000 overshoot can trigger a $386,000 bill
A New York taxable estate of $7,500,000 — just $150,000 above the $7,350,000 exclusion — falls in the phase-out band and owes roughly $386,000 in New York estate tax. A slightly larger estate of $7,800,000, past the $7,717,500 cliff line, owes roughly $746,000 — the entire estate taxed from dollar one once the credit disappears.
No portability to soften the blow
New York doesn't let a surviving spouse add a deceased spouse's unused exclusion to their own. See Portability & Marital Deduction for what New York couples do instead.