Some seven million people—more than 10% of the population—now claim at least one or more sickness or disability benefits. The numbers are growing fastest among working-age people who should be powering the country’s economy, surging more than 60% in the past six years to 4.7 million from 2.9 million in 2019.

Not including healthcare, the country will spend more than £100 billion this year on all types of welfare benefits for the sick and disabled, about a third more than defense spending. The tab has surged by a quarter in just four years and is on course to hit £130 billion in the next four, according to the government’s fiscal forecasts.

Many of the newer disability claims are for mental-health issues like depression, anxiety and ADHD, which can be harder for the government to verify than a physical disability. Between 2017 and 2025, disability claims for cancer doubled. But benefits claims for all psychiatric issues surged fourfold.

One benefit, created to help those with disabilities be more mobile, allows people to give up part of their welfare cash handout in return for a new car lease every three years. It now accounts for around one in every seven new car sales in the U.K. Among those who got new cars last year: 40 people whose primary medical condition was tennis elbow, 50 with wheat intolerance and 320 with dyslexia, according to government figures.

The scale of the payout has become a scandal. No other western country has seen such a rise in disability claims. In the U.S., the number of people getting federal disability payments has fallen in the past 15 years. The most recent figures show some 10.6 million working-age people in the U.S. claimed one or both main Social Security programs for people with a disability, in a country with a population five times bigger than the U.K.

Overall U.K. welfare spending

Total £408.6B

£400

billion

300

FORECASTS

200

£130.61B

Other welfare spending

100

Support for disabled people and people

with health conditions

0

FY2013

'15

'20

'25

'30

Total £408.6B

£400

billion

300

FORECASTS

200

£130.61B

Other welfare spending

100

Support for disabled people and people

with health conditions

0

FY2013

'15

'20

'25

'30

Total £408.6B

£400

billion

300

FORECASTS

200

£130.61B

Other welfare spending

100

Support for disabled people and people

with health conditions

0

FY2013

'15

'20

'25

'30

Total £408.6B

£400

billion

300

FORECASTS

200

Other welfare spending

£130.61B

100

Support for disabled people and people with health conditions

0

FY2013

'15

'20

'25

'30

Total £408.6B

£400

billion

300

FORECASTS

200

Other welfare spending

£130.61B

100

Support for disabled people and people with health conditions

0

FY2013

'15

'20

'25

'30

Note: Excludes pensions and healthcare; In nominal terms; 2025 onwards are forecasts; Fiscal years end March 31; £1=$1.32
Source: Department for Work and Pensions

Andrew Barnett/WSJ

It’s also a litmus test of a pressing question facing the West: Is it possible for political leaders to rein in spending on ever expanding welfare states? 

So far, the answer seems to be no, increasing the chances that countries like Britain are inching toward a financial reckoning.  

‘Clearly not sustainable’

The U.K., like its European peers, is caught in a vicious cycle. 

Its spending is surging thanks to an aging population, greater defense needs, a costly green-energy transition and the swelling bill for welfare and debt interest. But its income is mostly flat, with weak economic growth.

The government has raised taxes and binged on debt, borrowing an extra £1 trillion since the pandemic. That strategy is running out of road.

U.K. borrowing costs are higher than any country in the Group of Seven, recently hitting their highest level since the 2008 financial crisis. A slow but steady exodus of wealthy Brits leaving for tax-friendly locales like Dubai has shown there are limits to how much the government can keep raising the tax burden, which is already at its highest level since World War II.

The surge in welfare spending is “clearly not sustainable on any level,” says David Coombs, head of multiasset investments at U.K. fund manager Rathbones. “It really is the big issue of the moment, and the bond markets reflect that.” 

Borrowing costs on Britain’s 10-year bonds have risen to 5.5% from 4.5% at the start of the year, adding a few extra billion pounds to the country’s running costs. The U.K. is paying more for its debt than spendthrift France or historical basket cases like Greece.

But across Europe, attempts to change the social safety net—now considered a birthright even as it becomes a fiscal albatross—is proving politically toxic. 

In France, attempts to trim spending on entitlements led the National Assembly to oust two previous prime ministers. Spain reversed a previous overhaul to trim its pension system. After Germany passed some modest changes to its unemployment and health benefits, furious voters have punished the ruling center-right party. 

In 2025, then U.K. Prime Minister Keir Starmer announced plans to tighten eligibility requirements for sickness and disability welfare in a bid to shave £5 billion a year off government spending by 2030. 

The backlash was so sharp Starmer abandoned the cuts. Investors, spooked that a government with a big majority couldn’t push through such a reform, sold off British government bonds, the pound fell sharply and the Chancellor of the Exchequer cried in Parliament.

Starmer was later ditched by the Labour Party, replaced this summer by the telegenic Andy Burnham, who has also pledged to deal with welfare—but not through what he calls “crude cuts.” 

Burnham will unveil his first budget later this month and is widely expected to include fresh tax hikes, which could put Britain’s finances on firmer footing but will further crimp economic growth.

A debate about welfare is raging in the party—captured by Pat McFadden, one of Starmer and Burnham’s top aides. In a leaked WhatsApp message last year, McFadden complained that every meeting he had with Labour lawmakers was about “Who can we tax in order to pay benefits to others?” 

McFadden, who oversees the department in charge of handing out welfare, has promised changes to the system. Burnham’s own long-term vision is an unabashedly socialist overhaul—and expansion—of the state, even as he’s acknowledged the fiscal challenges.

If the British government wants to gain investor trust and lower borrowing costs, it needs to show it can make politically painful spending cuts to areas like welfare, says Andy Haldane, a former chief economist at the Bank of England and ex Burnham adviser. 

“The fiscal Achilles’ heel of this government thus far has been its unwillingness and/or inability to cut public spending,” he says. “The market now suspects that this is a traditional tax-and-spend socialist government with better TikTok videos.”  

Mission creep

Across the European Union, government welfare spending has steadily grown from just 10% of economic output in the early 1960s to an average of 27% today, compared with about 21% in the U.S.

Disability and sickness payments in the U.K. show how the system sprawls. 

Britain’s postwar government introduced disability payments to help offset lost wages for, say, a worker who lost a hand in an industrial accident. But over time, the system grew into an alphabet soup of programs. Some are aimed at people who are too sick to work. Others are broader: Personal independence payments are a cash handout for anyone—rich or poor, working or not—who has an illness or disability to help cover higher living costs.

U.K. benefit expenditure to support disabled people and people with health conditions, by age group

£150

billion

Total £130.61B

FORECASTS

100

Pensioners

50

Working Age

Children

0

FY2013

'15

'20

'25

'30

£150

billion

Total £130.61B

FORECASTS

100

Pensioners

50

Working Age

Children

0

FY2013

'15

'20

'25

'30

£150

billion

Total £130.61B

FORECASTS

100

Pensioners

50

Working Age

Children

0

FY2013

'15

'20

'25

'30

£150

billion

Total £130.61B

FORECASTS

100

Pensioners

50

Working Age

Children

0

FY2013

'15

'20

'25

'30

£150

billion

Total £130.61B

FORECASTS

100

Pensioners

50

Working Age

Children

0

FY2013

'15

'20

'25

'30

Note: Data shows spending on benefits for disabled people, people with health conditions and their carers; In nominal terms; 2025 onwards are forecasts; Fiscal years end March 31; £1=$1.32
Source: Department for Work and Pensions

Andrew Barnett/WSJ

PIP was meant to help with things like modifying homes or cars for wheelchair access. When the benefit’s precursor was created in the 1990s, the government thought a few hundred thousand would claim. Today one in every 12 people is getting disability checks. The program now covers people living with a range of physical and mental health issues, including anxiety, ADHD, depression and even acne. 

“I think people broadly agree the system is now doing things it was not intended to do,” says Paul Johnson, an expert in fiscal issues at the University of Oxford. “It’s not immediately clear, for example, why someone with depression or anxiety necessarily has higher living costs.” 

In deprived areas, particularly former industrial centers like Liverpool, a significant number of residents depend on welfare. In Walton, a Liverpool suburb that ranks as one of Britain’s most deprived neighborhoods, around 1 in 2 households claim welfare, and 1 in 5 working-age residents claim PIP.

“People aren’t working around here because they can get on PIP, so they sit around and do drugs and drink,” says Stephen Walker, a 65-year-old drummer who helps manage a Beatles memorabilia store, as he strolls through Walton on a recent day. “It’s unfair. I work and pay my taxes.”

Walker acknowledges some people do need the help—including three of his grandchildren, who are on PIP. But he says too many people just use it to top up their income and don’t get jobs. 

Charities say the welfare payments are a relief for people who’ve seen food and heating costs soar in recent years. Britain’s Conservative government in the 2010s cut unemployment benefits to try to spur people back to work, but it ended up causing extra hardship at a time of weak economic growth. People started claiming disability benefits instead. 

“People don’t just come in and go, oh, you know, ‘Jackpot. I’ve got an ADHD diagnosis. Gimme, gimme, gimme.’ It doesn’t work like that,” says Mick Blakeley, head of operational development at Citizens Advice Liverpool, a charity that offers advice on issues like claiming benefits.

Total number of Brits granted personal independence payments by select type

5

million

Other

Musculoskeletal disease (general)

Total as of July 4.09M

Psychiatric disorders

4

3

2

1

0

2019

'20

'25

5

million

Other

Musculoskeletal disease (general)

Total as of July 4.09M

Psychiatric disorders

4

3

2

1

0

2019

'20

'25

5

million

Other

Musculoskeletal disease (general)

Total as of July 4.09M

Psychiatric disorders

4

3

2

1

0

2019

'20

'25

5

million

Total as of July

4.09M

Other

Musculoskeletal

disease (general)

4

Psychiatric disorders

3

2

1

0

2019

'20

'25

5

million

Other

Total as of July

4.09M

Musculoskeletal

disease (general)

4

Psychiatric disorders

3

2

1

0

2019

'20

'25

Note: Cumulative data
Source: Department for Work and Pensions

Andrew Barnett/WSJ

Eleonore Paxman’s three children are all on disability welfare. Noelle, 31, has Type 1 diabetes, retinopathy and ADHD. Coco, 18, has autism and OCD, and Benjamin, 15, has pathological demand avoidance and ADHD. 

Paxman, 52, says the money has been a godsend, especially after her husband Jon went deaf and lost his job as a music arranger. She gave up work to home-school her two youngest children, which the couple felt was necessary after Benjamin spiraled when he first went to school at age 4 in their London suburb. 

Paxman, who also has ADHD, says things got so tough trying to juggle everything that she became suicidal. “Without the help, we’d be in big trouble,” she says. 

While the system genuinely helps people in need, it is also open to abuse. The claims don’t need a doctor’s backing; they are based on whether a person can carry out a range of everyday activities. 

The Department for Work and Pensions assesses a claimant’s form, followed by an interview. During the pandemic, the vast majority of interviews moved from in-person to over the phone or online, which critics say makes it harder for the government to tell which cases are real. 

A cottage industry of charities and consultancies have cropped up to help claimants navigate the benefits claim system, which can be both byzantine and, critics say, gamable. 

AI virtual assistants like “Pippin the PIP Benefits Support Worker” help fill in the forms. Reams of videos on TikTok offer tips on how to claim. One YouTube video, “Unlock The Secret Steps for WINNING your PIP claim,” has more than 465,000 views.

On average nearly 1,000 people a day are being put on PIP, according to government figures.

‘You get knocked back’

The problem for the British state is that the pool of people who could claim PIP is huge. A government survey published in 2024 found that a quarter of working-age Brits could be technically classed as disabled. 

The financial incentives to claim are significant. For example, a young person living outside London can claim around £900 a month on unemployment and housing benefits. If they are classified as being too sick to work and also claim PIP, that increases to around £2,000, tax free. If you work 40 hours a week in a minimum-wage job in the U.K., you take home £1,880 a month after tax.

Standing on Walton’s main street near a fried chicken shop, Morgan Price, 22, is one of a million young Brits who aren’t in school, don’t have a job and aren’t training for one. Price and her boyfriend make ends meet thanks to subsidized housing and unemployment benefits of about £650 a month.

Walton is one of Britain’s most deprived neighborhoods—and one of its disability-claims capitals.

For young people like Morgan Price, who has few qualifications, finding work is difficult.

Walton is one of Britain’s most deprived neighborhoods—and one of its disability-claims capitals. For young people like Morgan Price, who has few qualifications, finding work is difficult.

Recently, Price was classified as suffering from post-traumatic stress disorder after experiencing abuse growing up in foster care. She now gets an extra £300 a month in PIP payments to cover costs related to her condition. 

“You get knocked back and then the only way you can support yourself is by claiming benefits,” she says. 

Price says she has few qualifications and struggles to get work, especially now that she’s pregnant. Her boyfriend, who has a criminal record, has given up looking for a job. 

How many of her friends are working? “I couldn’t count them on one hand.”

The U.K.’s youth inactivity rate used to be middle of the pack in Europe. By last year, only Romania recorded a higher rate of young people not in employment, education or training. 

The number of them on welfare is raising alarms in government circles that they could become lifelong wards of the state. Some 40% of new PIP claimants are working, a number that drops to 25% after two years, according to the government. 

In Liverpool, like many postindustrial areas in Britain, there is a long legacy of welfare as a short-term tool to buy social peace. The port city rode the age of empire only to plunge into crisis in the 1980s and ’90s from shifts in global trade, deindustrialization and Margaret Thatcher’s crackdown on unions. The unwritten understanding: London’s booming finance and services hub would send the checks up north to ease the pain of mass unemployment. 

Margaret Thatcher’s crackdown on unions hit cities like Liverpool, already struggling from shifts in global trade, especially hard.

Unemployment soared to 25% in parts of the city.

Margaret Thatcher’s crackdown on unions hit cities like Liverpool, already struggling from shifts in global trade, especially hard. Unemployment soared to 25% in parts of the city.Popperfoto/Getty Images, John Stoddart/Popperfoto/Getty Images

Dockworkers were signed off with sickness pay or put on the unemployment dole. Little effort was made to figure out what they could do instead. 

Three generations on, Liverpool has bounced back from those dark days but the legacy of welfare lingers.

“I think there’s a lack of understanding about how unskilled some of the most disadvantaged people are in Britain and that actually we would be much better off investing in their skills than just giving welfare,” says Alun Francis, the chair of the U.K. Social Mobility Commission, an independent body that advises the government. 

A recent report commissioned by the government showed that for every £25 the state spends on benefits for young people, it spends just £1 on employment support. 

Government officials are considering ways to tighten eligibility for young people and instead pay for extra training to get them into work. The Department for Work and Pensions, which is currently reviewing the system, says it’s spending a further £3.5 billion toward helping those with disabilities get jobs. 

A gateway

A short drive from Walton, Roy Pearman is reaping the fruits of PIP at the car dealership where he works. 

Customers who get PIP and are classed as having limited mobility can lease a car for no cash upfront—they simply forgo about £320 a month of “enhanced mobility” allowance. Included in the lease that the government pays for are all road taxes, insurance and car servicing. The car can be swapped in for a new vehicle every three years.

Motability ‘exists because there is a real market failure which we solve,’ CEO Andrew Miller says.

It’s also benefiting dealerships and car salesmen like Roy Pearman.

Motability ‘exists because there is a real market failure which we solve,’ CEO Andrew Miller says. It’s also benefiting dealerships and car salesmen like Roy Pearman.

The business that provides the vehicles, Motability, is now the country’s biggest car-leasing company. Last year 860,000 people in the country had a Motability car. 

At the dealership, some 60% of the Fords and high-end BYD electric cars sold are Motability. “There is nothing like it anywhere else in the world,” Pearman says. 

Until last year, a small extra fee allowed PIP claimants to lease luxury cars like BMW and Mercedes-Benz. The system was tightened following an outcry. 

Pearman, a cheerful 73-year-old, holds up a sheet of paper listing 26 cars he sold in August. All but one are Motability. None are modified for disability. 

Across the U.K., only one in 10 cars sold under the scheme are modified for a disability. Motability says around 40% of its disabled customers don’t drive themselves, so don’t need adapted vehicles. 

“The scheme exists because there is a real market failure which we solve,” Motability Operations CEO Andrew Miller says. 

PIP is particularly valuable because it is a gateway to other incapacity payments and can remove a cap on the total amount of unemployment or housing benefits a family can claim.

Since the pandemic, far fewer PIP recipients have been reassessed and deemed healthy again. Britain’s Channel Four network found one man who’d been trying, unsuccessfully, to get himself off PIP for three years, saying he was no longer depressed. 

It doesn’t go so well for everyone. Wieland, the Cancún vacationer, was prosecuted after an anonymous tip and pleaded guilty to fraud earlier this year. While she has to eventually give back some £23,000 in welfare money, she was spared jail. Her lawyer told the court Wieland didn’t realize that receiving the payments meant she wasn’t allowed to actually go outside.

St Andrews Community Network sees local need first-hand.

CEO Tony Shepherd says the government has done little to help people get off the welfare conveyor belt.

St Andrews Community Network sees local need first-hand. CEO Tony Shepherd says the government has done little to help people get off the welfare conveyor belt.

Tony Shepherd, a former Goldman Sachs banker who now oversees the Liverpool charity St Andrew’s Community Network, says the government has built a conveyor belt for getting people on welfare, with little help to get them off again. 

There’s a long waiting list for things like state-funded mental-health support that could help people get back to work, he says. There’s also a lack of jobs. 

Around him, staff work the phones giving debt and benefits advice to locals. A chart on the wall totals the extra benefits they helped people claim this year. Crates of tinned food sit in a pantry ready to be shipped off to local food banks. 

“It’s a sticking plaster,” he says, using the English term for Band-Aid.

Corrections & Amplifications
Some benefits recipients forgo part of their welfare payments in exchange for a car lease. An earlier version of this article omitted the word “lease” in the first mention of the car program. (Updated on Oct. 12)

Klaas Verplancke for WSJ

If you don’t own a pair of so-called high-stack or max-cushion running shoes yourself, no doubt you’ve seen others wearing them, whether at the gym, on trails or just knocking about town. Sandwiched between the tire tread-like outer sole and nylon upper is as much as 2 inches of soft and springy foam, which gives these shoes both the look and feel of walking around with mini-mattresses on your feet.

It all started back in 2010 with the introduction of the Hoka line of max-cushion shoes, which led other brands to develop similar styles, each stacked with its own patented lightweight foam. Now it is difficult to find running or walking shoes that aren’t raised on a platform of puff, some with the added oomph of a layer, or plate, of carbon fiber.

While max-cushion shoes may feel super comfy, and can improve running efficiency and performance if embedded with a carbon plate, there are concerns among podiatrists, orthopedists, kinesiologists and sports-medicine doctors about the long-term effects, not only on your feet, but also your ankles, knees and hips.

“They change people’s biomechanics in a way that can be unpredictable, and brings up the question of potential injury risk,” says Dr. Adam Tenforde, director of running medicine at Mass General Brigham’s National Running Center.

A matter of mechanics

The problem comes down to basic biomechanics, says Dr. Kenrick Dennis, a podiatrist in Houston who served as medical director for the Houston Marathon.

“If you are standing on that marshmallow, it allows your foot to torque in and out a little bit more, the leg rotates to follow it, and that rotation is translated through the ankle, the knee and the hip,” he says.

It takes a bit longer to sink into the cushiness and subconsciously find your balance before you push off again, similar to the extra effort required when walking on sand. The wobbliness, he says, plus the added height of max-cushion shoes, also increases the risk of twisting an ankle or falling.

Moreover, max-cushion shoes diminish proprioception (awareness of where you are in space), since you have less sensory feedback of where you are vis-à-vis the ground.

A number of civil lawsuits have been filed against shoe manufacturers by track stars, including an Olympian, who allege, among other things, that wearing high-stack shoes with carbon plates caused injuries that derailed their careers. Nike faces one such suit in California Northern District Court. Puma—the parent company as well as some of its divisions and partners—was named in three cases filed in Massachusetts Superior Court.

Nike declined to comment on pending litigation, but in court filings the company denies its product is “defective and unsafe for its intended purposes” and neither “caused injury and/or contributed to the risk of injury.” Puma said in a statement that it strongly denies its shoes cause injury. The company is further pursuing a countersuit against its three accusers in a German court.

While the suits focused on shoes that included a carbon plate, Tenforde says max-cushion shoes can modify biomechanics independent of that feature. Hoka didn’t respond to requests for comment about safety concerns.

Of course, back when barefoot running was the rage in the mid-2000s, alleged injuries caused by zero-stack, or “barely there,” shoes resulted in lawsuits against manufacturers.

“The pendulum has swung from the barefoot shoes to now having a marshmallow under your foot,” says Dennis, the Houston podiatrist.

Proponents of max-cushion shoes, particularly those with an embedded carbon plate, point to studies that suggest the shoes improve running economy and performance by 4% and 2%, respectively. A 2023 review published in Sports Biomechanics says that every world record from the marathon to 5 kilometers has been broken by athletes wearing these kinds of shoes. The comfort and springy design may allow athletes to tolerate higher training volumes or intensities.

“If a shoe makes running easier, you will run faster,” says Dr. Laurent Malisoux, a sport and physical-activity research leader at Luxembourg Institute of Health. “But people should remember that if they get an injury, it’s because they probably ran too much, too fast or too soon, not because of the shoe.”

Stressing the muscles

Nevertheless, concerns remain. A 2018 study published in Nature indicates max-cushion shoes actually increase the total load on muscles, bones and joints compared with more-moderately cushioned shoes in part because the foot is on the ground longer.

“You’re hitting the ground with the same magnitude of force,” says Dr. Daniel Lieberman, a Harvard evolutionary biologist whose research focuses on how modern footwear has altered human biomechanics. “But you’re spreading that force over a longer period of time.”

Your leg also appears to stiffen more when you land, intensifying the jolt, according to the authors of the Nature study. If there is a carbon plate in the shoe, it can help you spring back into the air a bit faster, but Lieberman says more research is needed to determine whether the total load is larger than in more moderately cushioned or minimalist shoes.

While max-cushion shoes may feel great initially, repetition of these minute wobbly, twisting moments plus the extra mechanical load on muscles, tendons, joints and bones could lead to injury in the long term, critics say. During a mile run, each foot will strike the ground on average about a thousand times. Running 20 miles a week adds up to a million foot strikes a year.

There is also the concern that the squishiness of max-cushion shoes and/or the location of the flex point, particularly if there is a carbon-fiber layer, may also shift where on your foot you land and push off. That might make you more vulnerable to foot fractures, according to a 2023 analysis of high-stack running shoes with carbon-fiber plates published in Sports Medicine, with Tenforde as the lead author.

Scott Christensen, lead endurance instructor for USA Track & Field, says while he appreciates the potential performance-enhancing qualities of bouncy foam and carbon springboards, “everything has a cost-benefit ratio to it.” One of the more counterintuitive costs, he says, is the shoes’ exceptional comfort. Runners don’t get as sore, which is the body’s way of saying: Hey! Back off before you do damage.

“As a coach, I want soreness,” Christensen says. “I depend on soreness in my athletes. Soreness is the governor of training.”

Making good choices

So, what is a person to do when confronted with a wall of shoes in a run shop or sporting-goods store? “The answer is there is no one answer,” Christensen says. People have different physiologies, exercise regimes and injury histories which might dictate not only level of cushioning, but also support, stability and heel-to-toe drop of the shoe.

Whether you’re a runner, walker or maybe someone whose job requires you to be on your feet all day, the best shoe is the shoe that fits. You may think you’re wearing the right size, but a 2018 study in the Journal of Foot and Ankle Research suggests as many as 72% of people wear shoes that don’t accommodate either the width or length of their feet. Your shoes shouldn’t hurt or feel uncomfortable either during or after physical activity.

And don’t pay attention only to the pillowy feel under your feet, Dennis says. Test your ability to maintain balance and coordination in the shoes by doing things like raising up on your toes and holding and then rocking back on your heels and holding, as well as doing quick turns and pivots. Notice any additional workload or twisting moments demanded of the joints and muscles in your legs and hips. Also listen to your footfall. It should be light and have a steady, crisp cadence—no clomping, scuffing or shuffling, as can happen when you have too much bulk under your feet.

Beyond that, Christensen’s advises training in more than one kind of shoe, varying amount of cushioning and stack height. The combination will vary stressors on your body and reduce the chance of repetitive foot strike and motion injuries.

Dr. Stéphane Bermon, director of the health and science department at World Athletics—the international governing body for track and field, cross-country running, road running, race walking, mountain running and ultra running—is also a proponent of the shoe-rotation strategy, but he cautions to introduce any new shoe “very, very progressively” to avoid injury. Maybe running or walking in a new kind of shoe once a week for one week and then twice a week the following week, and so on.

“In biomechanics, in human physiology, what kills you is routine,” Bermon says. “Whether it’s your bone, whether it’s your muscle, whether it’s your tendon, you have to challenge yourself every day with different things.” In shoes, just as in life, “There is nothing worse than monotony.”

Write to reports@wsj.com

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Justin Cormack, who worked on MirageOS and Unikernel Systems back in the day, has been noticing what I've been noticing: people are discovering (or rediscovering) unikernels again. He's running a series of conversations on the topic for his newsletter, and I was first up. He emailed me, and five minutes later I was talking to him from the pub with a stein of beer in hand. We went deep on Mirage, Orleans, Haskell, Nix, Cursed and a whole lot more.

Here's the gist, written up properly, with chapter links at the bottom if you want to jump to a specific part of the conversation. Justin's edited transcript is over at Ignore Previous Directions.

Unikernels were hard. Key word: were. Now we have AI.

what a unikernel is, and why they were hard

I first ran into unikernels around 2015. I'd staffed up a team of Haskellers and gone pretty deep on functional programming. Where there are Haskellers, there are OCaml programmers, and from there you find MirageOS. Great idea. I played with it back then.

A unikernel is the idea that your application is the operating system. There's no userland. If you want a web server, DNS, or to send an email, there's nothing you can fork or spawn. You have to write those things as libraries in your application.

That was the friction. Justin remembers it well: when they were building Mirage, they had a TCP stack and an HTTPS stack, but there was almost nothing for storage. They were pulling drivers out of NetBSD because they could run them in userspace. It was hard back then.

There's a lot of dogma in our industry. Nix is hard. Bazel is hard. Unikernels are hard. Yes, they were. These hard concepts are now in the model weights. All you've got to do is prompt for them and, cognitively, get rid of the dogma that they're hard.

the operating system is design debt

Every application that isn't a unikernel was built on the assumption that there's an application, and then there's an operating system underneath. Why do we even have an operating system? Because forty years ago there was a human operator. I've done IBM 5250, AIX, Solaris, and mainframes. The multi-user operating system exists because a person sat in front of it, and then we put the application on top.

I consider that design debt, and here's why it matters right now. Applications get popped. They were getting popped before AI. Someone pops the userland application and gets a shell. That shell is a VIP butler service for exfiltration.

With a unikernel, the attack surface is much smaller. If the functionality isn't in the application (the operating system), then the attacker is screwed. There's no next hop.

Justin pushed back here, and fairly. Attack-surface reduction is something people are very fuzzy about. You can remove the shell from a Linux container, but almost every Linux environment still has something that's effectively an interpreter. You can execute a new program without a writable filesystem. You've still got memory safety and gadgets to worry about.

All true. But look at what we've been doing for twenty-six years. The earliest adage I remember from the SunOS and cgi-bin days was "don't put the compiler on production." Then came build containers and production containers. Then Chainguard. We keep chipping away at the attack surface, instead of going in the opposite direction and ensuring there is no attack surface.

And this is the bit people miss: if there's no shell and no interpreter, there's nothing in the model weights that knows what to do next. That turns a drive-by (pick your framework's RCE of the week and you've got a shell, and the model weights know what to do with shell access) into a targeted attack that needs your source code.

you can just port the missing libraries now

The classic objection: your unikernel needs to talk to Stripe, and OCaml doesn't have a Stripe library. Before AI you'd sigh and write it. Now? Run a loop to port the Go library to OCaml. Here you go: Stripe in a unikernel.

Justin had a great example of the same thing. He'd been building minimal Linux OS images for appliances, which is halfway to a unikernel anyway, since you're only running one application as PID 1. He needed to make an XFS filesystem. Rather than drag in xfsprogs and everything it brings with it, he sat down with an agent and had it write mkfs.xfs in Rust, producing byte-for-byte identical output, with every flag interpreted. It reverse-engineered the on-disk formats one by one, with tests across block sizes. It took a few hours.

That works because the original tool is a golden oracle. Generate filesystems at different sizes with both implementations and diff them. Port the tests across. Automate it.

Storage was the other big gap. Most workloads these days are cloud-shaped, even on-prem, so take the turbopuffer approach: S3 as your primary, infinitely growable storage, with a local NVMe block cache and an LRU (or whatever caching algorithm you like) for the hot bits. Justin is a massive "S3 for everything" fan too. As long as latency isn't the constraint, you get infinite storage with multi-user access, and you can build everything on it.

nix machine tests and overlays

Justin had been experimenting with Nix too, and was surprised that the first time he got an agent to prototype an OS, it built all the tests into flakes.

Nix the language sucks. Nixpkgs is great. NixOS machine tests are the bee's knees: you write a test that spins up a fleet of machines and exercises the interaction between your network rules and your application. It's the thing people don't know about.

And when something upstream is broken, or there's a supply chain problem in your dependencies, that's just an overlay.

If you have to tool-call a human, also known as "Dear Maintainer", who might be on holiday or might have abandoned the project, and wait a day, two days, or even five minutes, that's not AGI.

We're building recursive products here. Agents need the ability to modify the world as first-party source, not as third-party bundled binaries. We're going back to the contrib folder and Unix patches.

if you care about security, you have two choices

Justin asked what unikernels still need for people to discover them. Honestly, it's this. We've raised two generations of developers who don't even know they're a thing.

If you deeply care about security, there are really two choices:

1. You're sending satellites into space, and you should probably use seL4, a formally verified operating system. (I'm still a bit salty about the Australian government disbanding that team.)
2. Everyone else should seriously consider unikernels. Stop trying to harden something that is very hackable. Invert it and design from the other direction.

The other classic criticism is that many early unikernel designs ran everything at a single privilege level: your application in the same ring as the OS. In 2026, that's a prompt away from being fixed if you want ring separation. It's certainly more secure than praying to god your systemd cgroup configuration is right.

Think about how much time enterprises spend patching the world every time something new drops in Linux. Upstream now expects you to patch your kernel weekly. The week we recorded, someone popped KVM (essentially Firecracker, the core primitive we all thought was good sandboxing) and collected $50,000 from Vercel and a few other vendors. That is not much money for something that could root every managed cloud provider in the world.

spaceleans: a distributed unikernel operating system

About seven months ago, I went deep on unikernels to check whether my mental model was right. I showed Justin my Mirage folder, which holds all the functionality I needed to add.

• There was no way for a unikernel fleet to keep time, so I took an NTP client from another language and ported it. Then I built an NTP server based on RADclock and borrowed ideas from how TigerBeetle handles time: not one clock source but many, packaged as a library.
• Network stack, DNS, HTTP clients and servers, structured logging, OTel, Anthropic and OpenAI clients, and payments via Airwallex.
• A generic retry library for handling back pressure over HTTP, plus some PPX metaprogramming for fun.
• A PII wrapper at the logging boundary, so secrets and PII never leak through the logging subsystem. Every project should have one. It's pluggable; just use a functor.

And then the most cooked thing, which I'd never shown anyone before: Spaceleans, Microsoft Orleans ported to OCaml, running as a unikernel.

Orleans is a distributed actor system with transactions. You take many physical machines and merge them into one addressable heap. An actor always exists: await GetCustomer(), and if it isn't in memory, it gets rehydrated from a pluggable storage provider. You collapse your n-tier architecture into actors and stop caring whether something lives on machine A, B, C or D. The runtime handles it as an infrastructure primitive.

So in a weird sense, I built a distributed unikernel operating system out of actors, with a filesystem on top. Justin called it Erlang-esque, and he's right. I did all of it in a week. I'll probably never release it, but it falsified the idea that unikernels are hard.

sampling history

Being a little older means you can sample history, like an experienced DJ such as Carl Cox, who's been in the scene long enough to pull from previous repertoire and bring it forward. All of these ideas existed in the eighties. The models have read the papers. They've got TAPL and the most advanced type theory in their training data.

The thing that's lacking is people's curiosity and ambition to do these unhinged things, and the knowledge that previous records exist that can be sampled from.

How do we get people to try this stuff? We just do it. If you've got a turbo Lamborghini alien space rocket that's more efficient and more secure, good for you; you've got a leg up. Do cool things, attract curious newcomers, mentor them, grow. Same as it's always been.

Meanwhile, everyone else will be trying to Chainguard their Ruby on Rails application and managing AWS with fifty AWS-certified engineers, when two people with Nix and Hetzner would do. Eventually, it comes down to money. Higher-powered tools are more efficient, and efficiency wins, especially as AI collapses margins.

ocaml, rust, haskell and back pressure

Has OCaml's time come again? It's still going strong. A certain trading firm is using it very well. When I caught up with Yaron at the start of the year, I asked him whether OxCaml exists so their language extensions end up in the training data and lift the whole company. I got a very "no comment" smile.

For agents, OCaml is lovely. Functors between modules are beautiful. The .mli files, a typed header explaining how a module should work, are really efficient context for agents. opam and Dune are legitimately good. Hindley–Milner. And compile times are fast. I see no reason to do F# these days.

Justin has mostly been writing Rust, and agents are good at Rust. But compile time is the tax on back pressure. LLMs hallucinate, and when compilation is slow, each hallucination is expensive because you get fewer attempts per minute. Justin's S3 clone is about a million lines of Rust; with four agents compiling at once, they fight over disk and CPU. You end up spending more on fast machines than on tokens.

Haskell's type system is great, and the models do it really well. But I don't feel good running it in production: a space leak lives in the runtime state space and only shows up in production. Justin pointed out that the linear-type ideas in Rust came out of Haskell papers trying to solve exactly that. Then there's Zig's approach: allocate everything up front and never allocate again, which is what game devs did in the eighties and nineties. It's hard to persuade an agent to do that in Rust, though, because constant-memory programs aren't in its training set.

I think dependent types are the winner for next-generation languages. Anything that lets you codify more into the type system is more back pressure. You probably won't be surprised to hear I've got a fork of the Rust toolchain with dependent types. You can just do things now.

languages for agents, and what cursed taught me

The pace of language development has been held back by how fast humans can learn new concepts. Operator chaining is essentially sugar for humans. If agents write the code, we can lean on forty years of academic PLT research, as long as you know how to sample it.

The industry codified "do not make breaking changes" after Python 2 to 3. Justin knew companies with hundreds of people on that migration for years. I think that rule is no longer true. Ship a skill pack with the breaking change and let agents auto-migrate.

Justin asked what it actually costs to make a new language successful now. Go was the last language a company spent real money on, and it took a long time. I can answer that one.

Cursed was built with Sonnet 3.5 and 3.7, a deliberately underspecified prompt, and three months of running it in a loop. I started in C (not enough back pressure; I wasted too much time in Valgrind as the agent clobbered its own updates), then Rust, then Zig. Zig was a mistake; it would work today if I'd stayed with Rust. It cost roughly US$6,000, and I did it three times over. Compare that to what Go cost.

Now the real bit, the part that still scares me. If you allocate the context window correctly — a lookup table of the lexical structure and grammar — the model can program in a language that isn't in its weights. It's brute force and inefficient, but it works.

Think T-diagrams (tombstone diagrams). Lock down your grammar and lexical structure, reach a stage-two self-hosting compiler, ship a sensible standard library, and start the next training run. From there, you can reach a Roslyn-style self-hosted compiler with language services stupidly fast. Justin asked whether fine-tuning an open model would help bootstrap a language like this. It's not needed.

That was true a year and a half ago with much weaker models. It'll take just one programming language designer going all in with the good models to shock the world.

what next

As the pub was shutting, Justin asked what was on my mind. If you haven't read my latest post, go read it. If you manage people, create the space and time for them to experiment now, because within six months, leadership will ask you to put people on a vitality curve.

Yes, the labs trained on the commons. I hate that, and I get it. But you trade time and skill for money; employers have minimum standards, and those standards have changed faster than ever before in our industry. Be curious, learn how to build an agent, and go create beautiful stuff. We're in a renaissance.

It's a time-compression device. The more experience you have, the more you can sample. Not everything ships; some of what I showed Justin may never see the light of day. I use these projects as katas and redo them when the models get better.

But if you want to build something secure, seriously consider unikernels.

chapters

• 0:21 — discovering unikernels: Haskell to OCaml to Mirage
• 0:55 — what a unikernel is, and why it was hard
• 2:45 — hard was past tense
• 3:33 — why do we have an operating system?
• 4:17 — the shell is a butler service for exfiltration
• 5:12 — attack surface reduction is fuzzy
• 7:26 — don't put the compiler on production
• 9:13 — porting Stripe into a unikernel
• 9:54 — minimal Linux and mkfs.xfs in Rust
• 12:22 — S3 for everything
• 13:48 — Nix, machine tests and overlays
• 15:28 — tool-calling a human is not AGI
• 15:53 — seL4 or unikernels
• 16:56 — privilege rings
• 18:24 — weekly kernel patches and the KVM escape
• 19:38 — demo: the Mirage folder, NTP and time
• 22:05 — Spaceleans: Orleans in OCaml as a unikernel
• 25:31 — sampling history
• 26:52 — how to get people to try this: just do it
• 28:57 — OCaml and OxCaml
• 31:45 — Rust compile times and back pressure
• 33:06 — Haskell, space leaks and dependent types
• 35:13 — memory strategies: Rust, Zig and game devs
• 36:10 — languages designed for agents
• 37:41 — breaking changes and skill packs
• 38:53 — Cursed
• 42:36 — what Cursed taught me
• 46:47 — what's next: AI use is mandatory

Keep curious.

Under a blistering desert sun, the U.S. Army strained to show it had become a modern, AI-powered fighting force. 

Some blamed the heat. It was July in the Mojave Desert, and the thermometer climbed toward 110 degrees. Servers overheated. Batteries died and couldn’t be recharged. Soldiers drenched T-shirts in ice water and draped them over antennas that were on the fritz. 

Sgt. Ramontez Bennett’s drone from Anduril Industries was supposed to loiter overhead. Instead, the relentless glare forced it to land. “They gotta do something about it overheating,” he said. Plenty of America’s conflicts have played out in temperatures rivaling this particular July day. 

It wasn’t just the sun causing problems. “All it takes is one gust of wind and it’s on the side of a mountain,” he said. Behind the rugged peaks, drones lost their signal. 

Next to Bennett, another pilot prepared to launch a drone from Theiss UAV Solutions. After a prolonged wait to charge a drained battery, the aircraft took another 10 minutes to get airborne. Ukrainian soldiers can get a drone of about the same size off the ground in under a minute. 

Defense Secretary Pete Hegseth last year threw down the gauntlet with a directive to transform the Army into an AI-powered force equipped with drones and 3-D printers to quickly spin up weapons components, and directed the service to buy more software and startup tech. He instructed the Defense Department to stop looking for perfection in its tech, and buy off-the-shelf products that are good enough, stressing the urgency of modernizing. 

America’s investments in such weapons, some of which date to the Biden administration, have slowly begun to change the way it fights. In Iran, a war that has relied largely on older and expensive systems, the U.S. also used an unmanned boat made by defense startup Saronic to rescue a stranded helicopter crew. A drone modeled on Iran’s Shahed has been among the military’s most successful low-cost offensive weapons. The drone, called Lucas, costs $10,000 to $55,000 a unit thanks to an arrangement in which the Pentagon owns the design and farms out production to a group of manufacturers. 

Artificial-intelligence tools have also greatly accelerated intelligence analysis and target selection. The rapid evolution of the fighting in Ukraine shows how central such technologies will be to future wars. 

But America’s soldiers are still far from reaping the full benefits of cutting-edge autonomous weapons and AI systems, and haven’t been forced by necessity to quickly modernize as militaries like Ukraine’s have in the heat of conflict, current and former national-security officials said. Transforming a land-based fighting force with a history of slow technological adaptation into a nimble organization that makes the most of new innovations has been difficult.

A soldier enters a building during an assault exercise at Fort Irwin.

A soldier enters a building during an assault exercise at Fort Irwin.

Soldiers run into position during a combat training exercise.

Soldiers run into position during a combat training exercise.

Startups’ emerging new tech, most of which has never been to war, has at times proven to be too brittle in real-world applications, soldiers said. The Army is also in the throes of upgrading battlefield connectivity and communications, steps that are key to being able to fully capitalize on next-generation weaponry.

The military has held at least five press calls in recent weeks to talk about its modernization efforts. “There is a recognition that the battlefield is changing before our eyes,” Col. Gregory Merkl told reporters on one such call. “We are absolutely dedicated to transformation.”

Fort Irwin

Project Convergence brought 9,700 infantry soldiers to the desert for a 10-day, round-the-clock mock fight against an Army unit called Blackhorse, which stood in for China’s People’s Liberation Army. Media briefing materials billed the three-day July trip as a glimpse “inside the U.S. Army’s AI-enabled battlefield” and an opportunity for its leadership to demonstrate the use of AI apps, a data integration program, aerial and ground drones and sensor-loaded headsets in battle. 

In some of the moments meant to spotlight advanced technology on the battlefield, newly procured drones and developmental communication systems failed to perform as intended. 

Soldiers flew drones during limited windows and for half the maximum flight time to conserve battery and avoid losing them, and without full autonomy or any AI to assist. Chinese consumer drones could do the manual job a decade ago.

The battle offered the familiar scene of legacy warfare: green-suited soldiers kicking in doors, screaming above gunfire, weighed down with weapons from the last century. 

An Army spokesman for Project Convergence said the event was designed to allow for specific units to experiment with drones during pockets of fighting and learn about the tech, not to flood the airspace with autonomous weapons. The event was a way to “fact-check all the vendors that are coming to us” about the veracity of sales pitches from a crop of defense technology firms, said Alex Miller, chief technology officer to the Army’s chief of staff. 

Morning light filters through smoke and dust above the mock village at Fort Irwin.

Morning light filters through smoke and dust above the mock village at Fort Irwin.

The Army found during the exercise that the augmented-reality headsets referenced in its media invitation to Fort Irwin showed some deficiencies and the service is uncertain if it would move forward with them, a senior defense official at the training event said. Three companies have won contracts each worth more than $100 million to build the headsets.

While much of the tech there had already been awarded sizable Army contracts, officials and soldiers involved described it as experimental rather than essential new weaponry. 

“You take a piece of electronics and lay it out on a hot rock in 109 degree temperatures and try and make it work,” said Lt. Gen. Michael McCurry, one of the senior Army leaders running the event. “We’re seeing some of that.”

An Anduril spokesman said its drone overheated and that it had previously been tested in hot and cold temperatures. Following soldiers’ feedback, the company has prioritized making upgrades to improve the drone’s performance in extreme environments, he said. 

Theiss UAV Solutions founder Shawn Theiss said his drone typically launches within three minutes and that he received mostly positive feedback from soldiers at the exercise. Delays sometimes happen if soldiers aren’t trained, or if the communications parts, made by a separate company, have glitches, he said. The Theiss UAV drones there were more than three years old and batteries may not have been at peak performance, which can affect the launch, he said.

Some defense officials said the efforts would bear fruit longer term despite near-term stumbles.

Modernizing the military

Congress has long hammered the Army about modernizing its fighting. Congressional probes and government oversight reports have found that the Army has wasted billions of taxpayer dollars on fumbled new weapons programs, and suffered from inadequate training and failures in cybersecurity and data management. 

The Ukraine war brought the inadequacies into focus, bringing fully autonomous warfare to the battlefield with a tech proficiency that at times humbled the U.S. During battlefield drills held in Germany earlier this year, Ukraine’s drone operators took out a U.S. armored brigade. 

“The tech is moving so quickly that the U.S. military bureaucracy cannot keep up,” said Jonathan Rue, a former deputy assistant secretary of defense who played a key role in getting new technology into the Army, and is now a partner at firm MVP Ventures.

A soldier launches a drone.

A soldier launches a drone.

One soldier coordinates with another while operating a drone controller.

One soldier coordinates with another while operating a drone controller.

The last major Army transformation came about in the 1980s, when the service pivoted from Vietnam and built the force it would use in the Gulf War. It retrained, reorganized and brought in armored fighting vehicles, attack helicopters and modern air defense systems. 

The struggle now is to transform what recently ousted Army Sec. Dan Driscoll has called a “calcified bureaucracy” in preparation for a technologically sophisticated adversary—China. Driscoll departed in September, following disagreements with Hegseth. 

Daniel Goure, a former military analyst with the Lexington Institute who has held numerous war college teaching positions and roles in the Defense Department, said the Army’s history of modernization efforts are “almost unblemished by success.” He blames a tradition of risk aversion and a hierarchical organization.

Still, upgrades like the Army’s Next-Generation Command and Control system, used for AI-enabled planning and logistics, are a start. The system, with a $4 billion price tag in this year’s budget, allows troops to move faster and in a more dispersed fashion over longer stretches of battlefield, which is essential in modern conflicts, Army officials say. 

Starlink connectivity has meant that for the first time in his 19-year Army career, Lt. Col. Shawn Scott can radio a soldier sitting in an air-conditioned operations center at another end of the base, without cumbersome transmission poles. And new data-sharing technology has cut by two-thirds the time it takes Scott to plan and communicate missions.

The next step is bolstering the reliability of communications and data integration systems so AI-powered weaponry can actually help human fighters out in remote and austere conditions.

Capt. Alex Bayer reviews information on a tablet during a training exercise.

Capt. Alex Bayer reviews information on a tablet during a training exercise.

Soldiers maintain a defensive position at Fort Irwin.

Soldiers maintain a defensive position at Fort Irwin.

The Fort Irwin fighting climaxed with a predawn attack on a fabricated city, Razish, a relic of training for the wars in Iraq and Afghanistan. Stryker armored combat vehicles rolled down the hills. Smoke trucks attempted to obfuscate the view. Mortar rounds exploded and soldiers moved from one building to the next, firing blank bullets and pausing for the occasional smoke break.

A swarm of five small drones was forced to turn back as three Black Hawk helicopters carrying senior Army officials flew into the same airspace, squandering a rare high-tech moment they had come to see.

“It’d be a very dangerous time for us just to hand over everything to technology,” said Brig. Gen. Daniel Hibner, commander of the Army’s Joint Modernization Command. “It’s very much still a human endeavor.”

A soldier looks out at the terrain during combat training.

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