AB Trust的目的是estate tax portability, 就是早死的人的免税额留到晚死的人死时再用。联邦法律早就已经允许portabliity了，AB Trust可能在某些州有遗产税而且没有portability的情况下才需要，
加州没有遗产或者继承税，AB Trust根本不需要。
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What are the Pros and Cons of AB Trusts?
AB Trust Estate Planning can be most beneficial for couples who live in a state without a portability for exemptions. Essentially, an AB Trust could help these individuals avoid state estate taxes. AB Trusts can also help ensure your beneficiaries are not changed by your spouse after your death. Similarly, these trusts can help designate where certain assets will go if you need to protect them from your spouse for whatever reason.
For the most part, estate law has evolved enough to prevent the need for an AB trust if your intention is to prevent double taxation. AB Trusts can be challenging for couples as the deceased spouse’s assets are put into an irrevocable Trust. This can limit the flexibility and freedom available to the surviving spouse.
