# The Last Short Seller on How AI Could 'Unwind' the S&P 500 — Notes on Meb Faber Show EP640 with Carson Block
> Carson Block of Muddy Waters — the man Meb Faber calls 'the last short seller left in the world' — lays out an unsettling chain of logic on EP640: AI displaces high-paid knowledge workers, their 401(k) flows reverse, and the mega-caps that those flows inflated pull the S&P 500 down hard. Full summary, quotes, host and guest intros, and what we can take from it. A podcast listening note, educational.
Published: 2026-07-18
Locale: en
Tags: podcast, meb-faber, carson-block, muddy-waters, ai, sp500, short-selling, education
TL;DR: Carson Block (founder of Muddy Waters, 'the last short seller left') on Meb Faber Show EP640: AI could displace ~15% of US knowledge workers within three years — lawyers, accountants, coders, the high earners who fund 401(k)s. Those 401(k) flows have been the engine powering the biggest S&P 500 names. When the income stops and redemptions start, the flywheel runs in reverse and the mega-caps 'unwind hard.' He doesn't go naked short — he caps risk with put spreads and swaptions, betting credit spreads (near their tightest percentile ever, and nobody's worried) blow out. Inside: full summary, five quotes, host/guest intros, and six takeaways — passive flows cut both ways, being right on direction isn't the same as making money, read the footnotes for the linchpin trade, think in second- and third-order effects, and don't let your stance become your identity. Not investment advice.
> *The whole world is muddy, and I alone am clear;*
> *all men are drunk, and I alone am awake.*
> —— Qu Yuan, "The Fisherman" (Warring States, c. 3rd century BCE); translation mine
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If you only have 30 seconds: **a man who makes his living exposing frauds — the one Meb Faber calls "the last short seller left in the world" — lays out a chain of reasoning about AI that isn't the usual "is it a bubble." It's this: once AI actually succeeds, here's how it pulls the biggest names in the S&P 500 down, from the plumbing of fund flows up.** If you hold an index fund, this one's worth an hour. Here are my notes.
## The channel: The Meb Faber Show
The host, **Meb Faber**, is co-founder and CIO of Cambria Investment Management, a well-known name in quantitative asset allocation (he's behind ideas like Shareholder Yield, the Trinity Portfolio, and Global Tactical Asset Allocation). His podcast, **The Meb Faber Show**, is built around "helping you grow and preserve your wealth," and it runs a long line of interviews with investing minds and alternative-asset operators. It's one of the higher signal-to-noise English investing podcasts out there. Per regulation, he doesn't discuss Cambria's own funds on the show.
## The guest: Carson Block / Muddy Waters
**Carson Block** founded **Muddy Waters Research** and Muddy Waters Capital, and he's the best-known activist short seller of this era. He made his name unwinding a string of Chinese accounting frauds, then took the fight to Europe (the French hypermarket group Casino) and Japan (Nidec). His recent public shorts include **SoFi and Sport Radar**.
Meb's nickname for him lands well: **"the last short seller left in the world."** The trade has all but died off since the financial crisis. Meb calls short sellers "the immune system of financial markets," because the people who actually work out the fraud usually aren't the regulators. Carson now lives in Texas (he left California five years ago) and recorded this from a "bunker" in Sonoma wine country.
## The full summary
### 1. The core thesis: how AI unwinds the S&P 500 through fund flows
This is the heart of the episode, and Carson keeps stressing, **"I'm genuinely hoping to be wrong about this."**
- **AI displaces high-paid knowledge workers.** His estimate: roughly **15%** of US knowledge workers within three years — lawyers, accountants, coders, the highest-earning slice of the economy.
- **Unlike the GFC, there are no "green shoots."** These jobs don't come back at similar pay, and the new roles created don't offset the income lost.
- **The link is the 401(k).** Those high earners are the ones funding 401(k)s, and **401(k) flows have been the engine driving the S&P 500 — especially its largest names.** Add the demographics: boomers start taking redemptions too.
- **The flywheel reverses.** When these people lose their income, 401(k) net inflows go neutral, then negative. They sell taxable assets to pay the bills, then eventually redeem the 401(k) itself. So **the mega-caps that those flows inflated the most "unwind hard,"** with the S&P 500 and Nasdaq 100 hit first.
- **The endgame is deflation and a social reordering.** Aggregate demand collapses, AI turns "quite deflationary" at that point, and you head toward "a new social contract, a reordering of society."
He points to two things that make this different from past technology shocks:
1. **Past disruptions mostly hit jobs that were already on the way out. This time AI is aiming at industries and careers that were still rising** — white-collar, professional. (Meb's wry version: we used to tell blue-collar workers to "learn to code"; now the plumbers get to tell the coders to "learn to plumb.")
2. **AI models are now coding their own successors** — writing and testing the next generation, so capability climbs exponentially, and "we're not as humans going to be able to keep up with the pace of change."
### 2. How he plays it: capped risk, no naked shorts
Carson is explicit: **"We don't want to take any directionally short risk where our risk isn't capped."**
- **Equities: put spreads.** A structural bid keeps volatility depressed, so a naked short gets squeezed.
- **Credit: long spreads via swaptions.** Corporate and junk spreads sit at their **tightest percentile ever (about the 1st percentile)**, and almost nobody's bothered. When the shock lands and demand cracks, he expects spreads to blow out.
- **The second- and third-order effects are where it gets interesting.** He puts bond ETFs (LQD, HYG) in the second order (put spreads there), and in the third order, the municipal index fund **MUB** — its biggest constituents are exactly the states with ugly finances (California, New York, Connecticut, New Jersey, Illinois). In a real dislocation, the ETFs hit a liquidity mismatch and can't meet redemptions. His caveat: the central banks will step in and unfreeze it, so **"don't be a pig"** — take the dislocation and cover.
- **Honesty about timing.** He had his "epiphany" in February and expected the market to price this in faster than the GFC. Then the Iran war distracted everyone, and the "faster burn" hasn't shown up yet — but he thinks it's only delayed.
### 3. The "dirty secret" of the short-selling business
- **Activist shorting doesn't scale.** You find maybe **six times a year** a company that's both broken and badly misunderstood enough to publish on. He runs a few hundred million in AUM and says, "you could hand me a billion or two — I couldn't take it." The bottleneck isn't capital, it's how many real targets appear in a year.
- **Brand is the whole game.** Talk every day and you commoditize it; when a short activist speaks, it has to mean something.
- **Non-activist shorting without publishing has been a horrible business post-GFC.**
### 4. How he recalibrates his own filter
This part is the wisest stretch of the episode. Carson notes that short sellers see nails everywhere (they're all holding hammers), and the rates of depression and mental illness in the profession run high. Years ago he had a talk with himself: **"Am I looking at everything through a filter that's overly negative, overly cynical?"** Probably, he decided.
So he changed. **His team built a systematic momentum strategy that trades only inside the S&P 500**, started it in October 2024, and it's compounded "over 70% gross." He's also gone long **junior miners** — "smart people haven't wanted to work in mining since 2000, so there's edge there." His line: **"Are you living in the real world, or are you going to die that fiery death on Twitter?"**
### 5. Two cases in passing
- **SoFi (short).** He walks through a "fair value option" accounting treatment where loans get marked to $108–109 on day one, propped up by loan "sales" at around $106 that SoFi was quietly financing itself — and selling to an entity that appears to still be consolidated. Pull that linchpin, he argues, and it forces a restatement of roughly **$1 billion of previously reported EBITDA**. His verdict: "bleeding-edge financial engineering," maybe legal, right on the line.
- **China is "uninvestable."** Not a prediction that an index falls — the point is that **the quality of information is awful** (reporters and researchers who'd give you the real picture get removed), plus policy caprice, plus VIE structures where "you technically own none of these companies."
## Five quotes worth keeping
> **"Cynics always sound smarter. Optimists live in bigger houses."**
> The line the whole episode opens on — half a short seller's self-mockery, half clear-eyed truth.
> **"We're not as humans gonna be able to keep up with the pace of change... because these things are coding and testing their successors."**
> **"The dirty secret of the activist short selling model is that it's not scalable."**
> **"Are you living in the real world, or are you going to die that fiery death on Twitter?"**
> On the danger of getting trapped inside your own stance.
> **"What is risk? It's a BTFD."**
> For the two generations who entered markets after the GFC, "risk" just means buy-the-dip — because they trust the Fed to save it.
## What we can take from it: six lessons
1. **Passive flows are a double-edged flywheel.** The same 401(k) flows that pushed the biggest names ever higher can drain them just as mechanically. Index concentration risk isn't only a valuation story — it's a **fragility in the flow structure**, a dimension a lot of P/E-only investors miss.
2. **Being right on direction isn't the same as making money.** Even with high conviction, Carson caps risk with put spreads and swaptions instead of going naked short — because a structural bid depresses vol and the timing is impossible to pin. **How you express and size a view matters more than whether the view is right.** That's the same discipline as selling judgment, setting a stop, and avoiding negatively convex payoffs.
3. **Spreads at their tightest ever, and nobody's worried — that's an ignored tail.** When everyone is on "buy-the-dip, the Fed will save it," the asymmetry favors the skeptic. Insurance is cheapest when no one wants it.
4. **Think in second- and third-order effects, not just the first.** The interesting trade isn't "short Nvidia" — it's the second and third order of the fund flows (bond ETFs, munis, aggregate demand, deflation). The headline is a starting point, not the analysis.
5. **Read the footnotes and find the linchpin trade.** The point of the SoFi case isn't to shout "fraud" — it's that **one small circular transaction can hold up an entire pyramid of marks.** Gray-zone financial engineering tends to sit right on the legal edge; the forensic value is in tracing that one load-bearing piece.
6. **Don't let your stance become your identity.** Carson's best quality isn't that he's bearish — it's that he's honest about his own bias and actively added momentum and mining longs. Meb quotes Adam Grant, and it fits: **"the hallmark of an open mind is not letting your ideas become your identity."** That's the discipline of hunting for disconfirming evidence.
## Go listen to the original
However detailed my notes, they can't compress the first-hand texture of Carson telling the Wirecard story (the former COO turned out to be a Russian GRU asset) or debunking the "it's all about connections" myth of doing business in China. **Listen to the full 50 minutes:**
- Official page (with full transcript): https://www.themebfabershow.com/episodes/0hoNFbxmuTg
- The Meb Faber Show EP640, "Muddy Waters' Carson Block on How AI Could Unwind the S&P 500"
- Carson / Muddy Waters: muddywatersresearch.com
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*This is a listening note and educational summary of a public podcast. The views are those of the guest and host, not this site, and nothing here is a recommendation to buy or sell any security, a price target, or investment solicitation. The shorting, options, and swaption strategies mentioned carry very high risk and are mostly institutional tools an ordinary investor can't execute — don't copy them. Investing carries risk; make your own decisions or consult a qualified professional.*