US spot Bitcoin ETFs took in the largest single day of 2026 on 21 September. Exactly how large depends on whose table you read — the two answers are $380m apart.
- Farside / SoSoValue: net inflow of $998.95m, the biggest day since 6 October 2025 ($1.2bn) and the biggest of 2026. IBIT $381.37m, ARKB $289.12m, FBTC $238.84m — 91% of the day between them.
- CoinGlass: $617.58m for the same session, described as September’s second largest.
We have not split the difference. Both numbers are printed here, because the disagreement is the first thing this post is about: when you quote an ETF flow, ask whose table it came from.
The ether side does not reconcile either. Spot Ether ETFs the same day: $269.98m on SoSoValue’s numbers (ETHA $110.06m of it), $147.11m on CoinGlass’s.
Leverage was rising the same day
Santiment put aggregate crypto open interest up 7.6% to around $156bn over the same period, with volume up 39%; news.bitcoin.com subsequently recorded total open interest above $159bn. On Coinglass’s coin-margined measure, BTC open interest went from 685,600 to 717,400 BTC, with a long/short ratio of 1.0612.
There is a distinction here that gets glossed over constantly. A spot ETF buys spot — it lifts the price of the spot leg and generates no funding at all. Rising perpetual open interest is leverage, and funding only prices the second one. Both kinds of demand showed up on the same day; only one of them can appear in the funding rate.
What funding actually did
Binance BTCUSDT on 22 September, three settlements: 0.007663% / 0.010000% / 0.002784%, totalling 0.020447% for the day. The 08:00 period landed exactly on the 0.01% baseline; the 16:00 period was among the lowest of the week.
Widen the window to 16 September 00:00 through 23 September 00:00 (UTC), 22 settlements: cumulative 0.151008%, mean 0.006864% per period, high 0.010000% (the baseline, touched six times), low 0.001021%, and not a single negative period.
Market-wide: on 22 September, 447 symbols settled 2,350 times, mean 0.001772%, median 0.005000%, 7.15% negative — slightly below the 8.89% recorded on 20 September.
What it means for a two-leg book
A spot-long plus perpetual-short book cares about exactly one thing: whether funding turned negative. It did not, this week.
But do not read that as “price went up so funding is high”. A mean of 0.006864% per period sits below the 0.01% baseline, which means most periods did not even reach it. A billion-dollar ETF session and double-digit percentage growth in open interest, and what came out the other end was an average still short of baseline.
What to watch
Two observable things. If open interest keeps climbing while funding does not follow, the new leverage is not one-sided. If funding instead starts printing at 0.01% period after period, that is longs beginning to pay a premium. We are not forecasting next week.
Sources
ETF flows: Farside Investors daily table and SoSoValue (session of 2026-09-21), and CoinGlass figures (as reported 2026-09-22). Open interest: Santiment (2026-09-21) and Coinglass via BlockBeats (2026-09-22). Funding rates from the per-settlement records in our FundingRateTicks table, as of 2026-09-23 00:00 UTC.