Pension conversion questions

[SunniD]

I recently changed jobs and now have option to cash out of my defined pension plan. Should I roll the lump sum into a traditional IRA with Vanguard now or wait until I FIRE (in a few years) then roll and convert the lump sum into a Roth IRA? If I do the Roth conversion after FIRE does it have to be done in one lump sum conversion or can I split the roll and conversion across a couple of years?
Thanks!

[MDM]

It's almost always better to convert from traditional to Roth over several years, thus minimizing the tax bite.

As to taking the pension lump sum now or later, how much will the lump sum change?

[MDM]

It's almost always better to convert from traditional to Roth over several years, thus minimizing the tax bite.

Yes, and that's the plan for my 401K when I FIRE.
And that's why for the pension I thought it would make sense to take advantage of the ability to roll the lump sum directly into a Roth then I wouldn't have to do a conversion ladder from traditional. But, to minimize the tax bite, can I break the lump sum up over a few years?

By "break the lump sum up" do you mean "have the employer give you partial lump sum payments, spread over several years"?  If so, that is up to the employer but I'd guess that is unlikely.  Even if the employer would do so, there seems little to no difference between that vs. having it all in a tIRA and doing traditional->Roth conversions spread over several years.

As to taking the pension lump sum now or later, how much will the lump sum change?

If I leave it in place with the old firm the lump sum grows by just over 4.5% per year.  Until I reach 65. But if I cash out I should be able to match those returns by rolling it into an IRA investing in VTSAX.

That's an asset allocation question.  4.5% is good for a bond return.