Whether a trust needs a tax ID number depends on the type of trust. A trust account that is “revocable” is still an account that can be controlled by the original grantor of the trust. Consequently, it’s going to be filed under the grantor’s own social security number or individual taxpayer identification number.
If the trust is irrevocable, on the other hand, it’s a separate legal entity. It cannot be changed by the grantor of the trust. The beneficiary would need to allow for any changes on their own end. Consequently, the irrevocable trust will need its own tax ID number, also known as an EIN. Though an “EIN” is technically an “employer identification number,” it’s also used for the purposes of tax reporting.
The trust account will need an EIN the moment it becomes irrevocable (transitioning from revocable state) or when it’s formed as an irrevocable trust. A trust becomes irrevocable automatically when the grantor passes on, as the grantor can no longer control the trust, although this situation can be complicated if there are multiple grantors.