Tipswatch.com, updated Oct. 13, 2022
The Social Security cost-of-living adjustment is based on an unusual inflation index – CPI-W – and is determined by averaging the indexes for July, August and September and comparing that number with the same average for the year before.
For 2023: Inflation from July to September 2022 was 8.7% higher than the same period of 2021, so the Social Security COLA will be 8.7% for payments beginning in January.
This will be the fourth highest Social Security COLA in history:
More information:
— September inflation report sets Social Security COLA at 8.7% for 2023 payments
Treasury Inflation-Protected Securities 
Yes, the purchase limit is not affected by an I Bond redemption. It remains $10,000 per person per year.