A charitable remainder annuity trust requires a separate tax ID because it no longer reports its taxes under the original grantor, nor does it report its taxes under beneficiaries. Luckily, an EIN isn’t difficult to get, and the EIN will usually be acquired when the trust account is opened.
Any trust account that is no longer in control of the grantor (an irrevocable trust) will need an EIN, because it’s now a separate entity from the grantor. There are revocable trusts that may still file under the original grantor and the original grantor’s social security number, but a charitable remainder annuity trust is not one of them.
The same reason that a charitable remainder annuity trust needs an EIN is the same reason that it’s a good tax vehicle; it pays its own taxes. Once the trust dissolves, it will extend the assets to the beneficiaries, and the beneficiaries will become responsible for taxes. The EIN will then no longer be necessary.