Bitcoin ETFs Erase a $586M Slide to End the Week Flat
The week in flows
US spot Bitcoin ETFs closed the reporting week of September 14 through 18 with net flow of +$6.1M — the flattest week bryptoflows has recorded in months, and one that hides a genuine round trip underneath it. Monday opened the week positive at +$159.9M, then the category fell for two straight sessions ahead of the Federal Reserve's rate decision: -$450.4M on Tuesday, September 15, and -$295.9M on Wednesday, September 16. By Wednesday's close the week was down -$586.4M. Thursday and Friday reversed almost all of it, with +$159.5M on Thursday — the session the Fed announced its decision — and +$433.0M on Friday, the strongest single day since mid-August. Net across all five sessions: six million dollars, essentially nothing, but only because two very large moves in opposite directions cancelled out.
The proximate cause of the midweek slide is well documented outside bryptoflows: the Federal Reserve raised its target rate 25 basis points to 3.75%-4.00% on September 16, its first hike since 2023, in a 12-0 vote with 16 of 18 participants projecting at least one more increase this year. Spot bitcoin ETFs recorded their largest two-day outflow in roughly two months heading into that decision, then turned net positive the same day the hike was announced as markets finished pricing it in — a sell-the-lead-up, buy-the-announcement pattern KuCoin's coverage and CryptoTimes' reporting on the same two sessions both describe in the same dollar terms bryptoflows tracks. Friday's rebound coincided with bitcoin itself clearing $80,000 for the first time in weeks; a same-day report put the day's net inflow at the identical $433M figure bryptoflows records, with Fidelity's FBTC alone taking in $311M.
bryptoflows' own rolling windows show the shape of that reversal without smoothing it away. The three-session average is now +$98.9M a day, and the five-session (weekly) average sits at essentially zero, +$1.2M. The ten-session window is still negative at -$28.2M a day, carrying the scar of the prior week's outflow streak, while the twenty- and sixty-session averages remain solidly positive at +$88.1M and +$40.6M respectively. Friday's session alone carried a z-score of +1.22, in the 86th percentile of all 690 sessions on record — a strong day in isolation, not just relative to a weak week. The category is now on a 2-session positive streak, its first since the reversal began.
Where the moves came from
No single fund defined the week the way ARKB defined the outflow week that preceded it, but two products did most of the offsetting work. BlackRock's IBIT was net positive across the week at +$120.6M, and Fidelity's FBTC added +$79.9M — together more than double the week's net total, funded almost entirely by Friday's session, when FBTC alone took in $310.7M and IBIT $108.4M. ARK 21Shares' ARKB was the week's largest detractor at -$141.9M, and Grayscale's legacy GBTC shed -$62.3M, both concentrated in the two Fed-week selling sessions. Morgan Stanley's MSBT added a modest +$13.2M and was one of only two products that never printed a negative session all week; Franklin Templeton's EZBC contributed +$4.6M. VanEck's HODL and Bitwise's BITB were both close to flat, at -$5.3M and -$2.7M. Invesco Galaxy's BTCO, Valkyrie's BRRR, WisdomTree's BTCW, and Grayscale's BTC mini trust reported exactly zero every session this week.
Breadth swung as hard as the dollar totals did. Tuesday's sell-off was the narrowest possible: five products reported a flow and all five were negative, zero positive. Wednesday was only slightly better, one positive against four negative. Friday inverted that completely — five products positive, zero negative, the broadest session of the week. bryptoflows' single-day concentration reading closed the week at a product HHI of 0.578, elevated by the standard of an even twelve-way split but unremarkable next to the near-total concentration a five-fund, all-negative session like Tuesday's implies. Life-to-date concentration is essentially unchanged at a product HHI of 0.407 and issuer HHI of 0.439, since one week of any description barely moves a two-and-a-half-year cumulative measure.
Zooming out
Cumulative net flow into the category since inception now stands at $55,229.7M, up marginally from $55,223.6M a week ago — this week's near-zero net is why the change is so small. The drawdown from the category's all-time cumulative peak of $62,735.9M sits at -$7,506.2M, or roughly 12.0%, essentially flat versus last week's 12.0% reading after that gap had widened the prior week. Period totals: week-to-date +$6.1M, month-to-date (September) +$313.4M, quarter-to-date +$4,025.3M, and year-to-date -$1,364.5M — a small improvement from -$1,370.6M a week ago, though 2026 remains a net-negative year for the category overall.
Strategy: no new filing, but a much wider cushion on an unchanged position
Strategy's treasury has nothing new to report this week. The company's most recent 8-K, filed September 14 and covered in full in last Wednesday's treasury piece, disclosed no bitcoin purchases and no bitcoin sales for the period ending September 13 — the company's own filing marks the period's direction as none. Holdings stand unchanged at 845,050 BTC against a $63.73B cost basis, or $75,412 average cost per coin, and no filing has landed since; the next is due around September 21. Financing capacity is likewise unchanged from the August 31 baseline at $44.34B of undrawn capacity across Strategy's five at-the-market programs, since no new shares have been sold under any of them in the two filings since.
What has changed is the price the unchanged position is marked against, and it moved sharply in Strategy's favor. Last Wednesday's treasury piece used a $76,180 close to put the position's cushion at roughly 1.0% above cost, the thinnest reading in months. Bitcoin has since rallied hard: a same-day report put bitcoin at $81,453.50 on September 18, and a separate report the same day had it at $81,256 — both above $80,000 for the first time in weeks. At roughly $81,300, the unchanged 845,050 BTC position is worth in the neighborhood of $68.7B against its $63.73B cost basis, an unrealized gain of about $4.9B, or roughly 7.8% — up sharply from last week's near-breakeven reading purely on price, with not a single coin bought or sold in between. As always, this comparison mixes bryptoflows' own SEC-sourced cost basis with an externally reported bitcoin price rather than bryptoflows' own candle feed, which remains unavailable in the site's source-freshness check, so it should be read as directional rather than exact.
MSTR's own stock moved even more than the underlying: reporting from September 18 put the shares up 16.2% that day to $153.92, up roughly 26% over the prior three weeks, with several sell-side desks reiterating bullish ratings. The same coverage ties part of that move to a bitcoin-related legislative development rather than the treasury alone: the House Financial Services Committee advanced H.R. 8957, the American Reserve Modernization Act — which would establish a federal Strategic Bitcoin Reserve — by a 28-21 vote on September 16, according to DailyCoin's reporting. The bill still needs a full House vote and Senate passage before it could become law, and nothing about it changes Strategy's own treasury this week — but it is a real, dated catalyst behind the mood this recap's numbers sit inside, not something bryptoflows' own data can measure directly.
What to watch
- Whether Strategy's next 8-K, due around September 21, shows a return to bitcoin buying, another sale, or a fourth flat-to-quiet filing.
- Whether Thursday and Friday's rebound extends the flow streak past two sessions, or the week turns out to be a bounce inside a choppier month.
- Whether ARKB's outflow was a one-off tied to the Fed-week selloff or the start of a repeated pattern in a fund that ran net-positive for most of its history.
- Whether bitcoin holds above $80,000, which would matter both for Strategy's widened cushion and for the ETF flow picture generally.
- H.R. 8957's path to a full House vote, and the MSCI index-exclusion consultation on Strategy, with comments due September 30 and a decision October 16 — both still open regardless of which way this week's flow or price moved.
Track the flow data live on the flow pulse overview and ETF flow dashboards, and Strategy's full treasury and financing history on the MSTR breakdown. Flow and attribution figures throughout are read directly from bryptoflows' own API — ETF flows from Farside Investors, Strategy detail from SEC filings — current through the September 18 close and the September 14 filing respectively. Bitcoin price figures in the Strategy section are sourced externally, as noted there, because bryptoflows' own candle feed was reporting unavailable at the time of writing. Retrieved and published September 19, 2026.