BlackRock files a buffer bitcoin ETF, and IBIT took $665m in a day

BlackRock filed on 19 October for the iShares Bitcoin Managed Protection ETF, ticker PBIT. It buys a buffer against falls and pays for it by giving up the top of any rise, and it does that with options written over the firm's own IBIT rather than over bitcoin directly.

“The Fund seeks to provide upside exposure to the iShares Bitcoin Trust ETF (IBIT) and/or similar bitcoin exposure up to an approximate limit, while seeking to provide a level of downside protection.”

— iShares Trust, Form 485APOS, 19 October 2026

How the buffer works

The mechanics sit in the prospectus. The fund sells out-of-the-money calls to fund higher-strike calls, which sets both a floor at roughly 90% of the reference value at a tranche's start and a cap above it. Three tranches run at once on staggered monthly starts, one expiring and one opening each month, with fixed income held alongside for interest. The floor erodes as the price rises after inception, so the protection is at its full size only at the moment a tranche opens.

We counted the windows

A ten percent floor is the number worth testing against bitcoin itself. We counted every rolling thirty-day window in the last 1,000 days of BTCUSDT closes. Of 970 windows, 155 fell by more than 10%, which is one in six. Over the most recent 365 windows the count rises to 99, or 27.1%, while only 59 of those same windows gained more than 10%. The deepest thirty-day fall in the set was 32.9% and the best gain 58.7%.

Read plainly, that says the floor would have been fully spent in more than a quarter of month-long stretches over the past year, and the cap would have bitten in about one in six. The structure trades a tail you feel often for a tail you feel less often, which is a defensible bargain and a different one from the way these products are usually sold.

What it costs is the one thing the filing does not say. The management fee appears in the document as a blank line, so the buffer has no price attached to it yet. Calamos, First Trust and Innovator already run defined-outcome bitcoin funds, and the analyst James Seyffart notes that BlackRock arriving in a category tends to make a splash.

The flow in the same report

The flow number in the same report is doing something else. IBIT took $665.2m on Monday against $66.37bn in assets, so the fund pulled in one percent of itself in a session. The whole sector netted $526.6m, which means the other eleven funds lost $138.6m between them, with FBTC down $83.6m and GBTC down $54.9m.

Put that against the month. October's running outflow stood at $617.17m before Monday, so one day of IBIT erased all but about $90m of it. The split inside the sector is the story we have been tracking all month, and it is the same concentration that made a single day take 68% of the year's net earlier in October. What settles PBIT is the first published cap and the fee that is still a blank.

Informational material, not investment advice. The window counts below measure how often bitcoin moved by more than the stated buffer, not what the fund would have returned, and the filing is a preliminary amendment.