Investors purchased Series I bonds in record numbers from the U.S. Department of the Treasury on Friday, just beating a key deadline to lock in a historically high rate of return.

I bonds are a nearly risk-free asset tied to the rate of inflation. They've proven to be a bright spot for investors amid declines in the broad stock and bond markets this year.

Investors had a Friday deadline to buy I bonds and lock in a record-high 9.62% interest rate for six months. The rate reset Tuesday, falling to 6.89% — still the third-highest on record since the bonds debuted in 1998.

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The Treasury sold $994 million of I bonds before the deadline on Friday — nearly as much in one day as during the three years from 2018 to 2020, when investors bought slightly more than $1 billion, according to Treasury Department figures shared Monday night. Investors opened 95,482 new accounts on Friday, also a record.

Investors purchased more than $3 billion of I bonds last week and almost $7 billion in October — which represent weekly and monthly records, too, according to the Treasury Department.

Investors opened 359,822 new accounts last week and 731,336 new accounts during October.

TreasuryDirect.gov — the website where investors purchase I bonds — crashed on Friday as the volume swelled. TreasuryDirect became "one of the most visited websites in the federal government" in the final days of the 9.62% rate window, the Treasury Department said Friday. It typically hosts just a few thousand concurrent visitors.

I bond rates shift twice a year based on inflation.

There are two parts to the rate: a fixed rate, which stays the same after purchase, and a variable rate, which shifts twice per year based on inflation. The Treasury Department announces new rates every May and November.

Investors may lock in the new 6.89% rate for six months by purchasing I bonds any time before the end of April 2023.

You can purchase the assets online through TreasuryDirect, limited to $10,000 per calendar year for individuals. You can also use your federal tax refund to buy an extra $5,000 in paper I bonds.