There is another (slight?) risk with TIPs. They depend on the government's definition of what the CPI is. The current administration has demonstrated a willingness to create their own reality and might choose a CPI that is less than actual inflation. That would be another reason to stick with 1-3 month Tbills where the price (and thus inflation) is crowd-sourced, as it were.

Yes, they could mess with CPI. But probably only at the margin. Presumably a period of generally higher inflation would have even a broken CPI going up somewhat faster. So that would be a small risk compared to the bigger risk of leaving yourself completely exposed to inflation as rolling T-bills would do. You would have no idea in advance what your real return would be over time, and (based on history) it would likely be negative.

For portfolio planning TIPS are a very different asset class, in some ways as different from bonds as bonds are from stocks.

The real risk in TIPS is possible fall in the US dollar--lower purchasing power of tradeable goods and services, which is most things. There are good reasons to think it might fall quite a bit, and other good reasons to think it might rise. If you're concerned about bounding that risk, one could buy a small portion of WIP, an ETF which holds a wide variety of non-US government-issued inflation protected bonds. It has gone nowhere for years, but it does go up (measured in US dollars) when the US dollar shrinks, almost perfectly (and almost by definition). YTM most recently reported as 6.8%. A chunk of UK, then 4% allocations to a lot of other countries. I'm not fond of fixed income funds, especially with .5% fees, but it would be a huge amount of work to replicate this yourself.

Jim