Hi and welcome to our site!
As you are US person (US citizen or a resident alien
purposes) - you are required to report all your worldwide income - so there will not be any changes based on your residency.
is essentially will be the same and tax rates
will be based on your total income, filing
status and deductions
You are taxed on full distribution
- but if you previously made after tax contributions - that part is recovered tax free,
However - - you might be able to use some tax treaty provisions and exclude some types of income
See the full document here
Specifically - see page 27 - ARTICLE 18Pensions
, Annuities, Alimony
(1) Subject to the provisions of Article 19 (Governmental Remuneration), pensions and other similar remuneration paid to an individual
who is a resident of one of the Contracting States
in consideration of past employment shall be taxable only in that State.
(2) Social Security payments and other public pensions paid by one of the Contracting States to an individual who is a resident of the other Contracting State or a citizen of the United States shall be taxable only in the first-mentioned State.
That actually means - you MAY claim tax treaty benefits
so your Australian pension will be taxable in the US and excluded from Australian taxation based on your US residency.
If you are living in Australia - that distribution will be taxed there and may be excluded on your US tax return.
Let me know if any clarification needed.