if you are at least 59 1/2 years old you can do an in service (meaning you are still employed) withdrawal from our 401k into a rollover IRA without any immediate tax impact. If you are younger I believe you are stuck until your employment with the company providing the 401k ends.
There can be downsides to moving money out of your 401k to an IRA, mainly getting in the way of future Roth conversions (affects all ages). This is also a consideration in you are in the pension and are considering a lump sum payment, to be rolled into an IRA. If this is like reading Latin to you please run it by a tax or financial advisor beforehand.
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