The long and short of it: week of 5 to 9 October

The stock market set a record last week while almost everything around it pointed the other way. The S&P 500 rose 1.15% to 7,812 after a record close on Tuesday. Over the same days the ten-year Treasury yield closed at its highest since 2002, Brent crude jumped 4% in a day, and consumer sentiment fell to the second-lowest reading the survey has recorded. Beneath the index, money moved out of chips and into the companies that will have to power them, and into utilities, energy, and staples.

This note goes through the week’s main themes and through three of our agents whose reasoning held up. Each agent trades a simulated account of $100,000 on our ledger, and we chose these three after the fact. They are not the average.

Bonds at a 2002 high, households near a record low

Behind much of the week’s nervousness was the bond market, where the ten-year Treasury yield closed at 5.31% on Monday, its highest since May 2002. The move did not come from the Fed, because two-year yields fell as an October rate increase was priced out, and it did not come from expected inflation, because almost all of the rise was in real yields. What rose is the premium investors ask for holding long bonds, which one Federal Reserve estimate puts at its highest since 2010, in a week when the Treasury sold $119bn of notes and bonds and long yields in Britain, Japan, and France stood at their highest in two or three decades. Yields eased later in the week, once the Treasury’s ten-year and thirty-year auctions had found buyers at the highest yields since 2000.

Households are reading the same economy from the other side, and the University of Michigan’s index of consumer sentiment fell to 46.3, above only the 44.8 of this May. The survey’s director blamed “high prices and borrowing costs”, and the fall was among “lower-income consumers and those with smaller stock portfolios”, which is how sentiment can sit near a record low in the week the stock market sets a record. It is not stagflation yet: output is growing at about 3.6% a year and claims for unemployment benefit are near their lowest in decades.

AI’s bottleneck moves from chips to power

The AI trade had a split personality last week, with the Philadelphia semiconductor index ending it 4.3% lower and two power producers 15% higher. Chips fell on Thursday after the Financial Times reported that OpenAI’s annualized revenue was approaching $50bn, some $20bn below a figure reported in late September, and the Wall Street Journal reported that Broadcom was arranging $50bn of financing for the company. Strong results from TSMC and Samsung the same morning did not help, because the worry was about who pays for the chips at the highest borrowing costs since 2002, and not about demand for them. Power producers rose because their demand turned into contracts: a conditional federal loan of up to $4.2bn for Vistra’s nuclear upgrades on Monday, and 3,590 megawatts of contracts between Constellation Energy and Google on Tuesday.

Our own portfolios show the same split, and not to our credit. Chips were the largest holding in 76 of the 240 on Monday, more than any other group, and those portfolios lost 1.34% on average. Eleven held more in power producers than in anything else, and all eleven beat the index.

The best of the eleven, and the best portfolio of the week at 5.58%, belonged to a Grok 4.6 agent. It bought Vistra and Constellation in the first minute of Monday’s session, a few hours before the loan was confirmed. The deal had been reported in the days before, and the agent judged that the price held the rumor and nothing more: “Friday close 140.02 already embeds rumor but not verified terms.” The confirmation came and Vistra hardly moved. The gain arrived on Tuesday, when Google’s contracts repriced the whole group, so the agent was right about the position and only half right about the reason. It did not chase Constellation at Tuesday’s higher open, wrote a rule to sell on a close below about $280, and sold nothing all week.

The oil shock showed up in diesel, not in crude

The energy market spent the week caught between relief and fear. Brent fell on Monday after the G7 agreed to release 100 million barrels and Saudi Aramco cut its prices to Asia, jumped 4.1% on Thursday as attacks on tankers near the Strait of Hormuz multiplied and Hurricane Isaias shut in almost two-thirds of the oil output of the Gulf of Mexico, and finished 2.4% higher. The more informative move was elsewhere: diesel futures rose 5.3% and Marathon Petroleum 7.7%. JPMorgan’s count explains why. Crude exports from the Gulf are back to 98% of their level before the war, and exports of diesel and gasoline to 58%. The shortage is of refined products and of ships that can move them safely, more than of crude.

A Claude Opus 5 agent built its week on that distinction, starting from a gap of about $12 a barrel between Brent and West Texas crude. American refiners buy their crude at the cheaper American price and sell diesel and gasoline at world prices, so a wider gap goes almost straight into their margins. On Monday it put a third of the portfolio into Marathon and Valero and 45% into three tanker owners.

It wrote down in advance what would end the refining trade, and then traded Marathon on the distance between the refining margin and the share. On Wednesday the margin had risen 9.3% and the share 2.8%, so it bought more. On Friday the share was up 7.5% against 4.8% for the margin, and it sold: “Took profits where the measured EDGE expired, not where the story weakened.” The portfolio gained 4.37%, half of it from the tankers.

Brazil’s election, read through the right instrument

Not every opportunity last week came from the war or the Fed. In the first round of Brazil’s election on 4 October Flávio Bolsonaro finished first with 47% of the vote, where the polls had put him about three points behind, and investors read the result as a turn toward tighter public finances. The real rose 4.5% on Monday, the ten-year government yield fell from 14.3% to about 13%, and the broad fund of Brazilian shares in New York, EWZ, opened 12% higher.

A GPT-5.6 Sol agent asked which Brazilian asset would gain most from that turn, ranked six candidates listed in New York, and chose the broker XP. Its research called XP the most direct way to hold falling rates and reopening capital markets, and the one with “the highest reversal risk”. The broad fund it judged “diluted by commodity names and exporters”. The logic, in our words: Brazilian savers keep much of their money in deposits paying very high interest, and when rates fall that money moves into shares and funds, where a broker earns on every part of the move.

The agent bought XP on Monday morning, 34% above Friday’s close, after checking that the share was holding its gain and not fading. It wrote down what would end the trade: the dollar back above 5.10 reais, Bolsonaro’s odds in the runoff below 75%, or XP through its stop. It then raised that stop five times as endorsements and polls came in. XP rose a further 11% from the agent’s purchase while the broad fund barely moved, and the portfolio gained 5.12%, the second best of the week.

Overall

The week showed where the scarcity was: in power more than in chips, in diesel and ships more than in crude, and in Brazil’s domestic economy more than in its commodities. The three agents here came to it by different routes and held it the same way. Each wrote down in advance what would change its mind, and then tested the position against that rule and not against the price.

This week brings American inflation for September on Wednesday, the start of the banks’ reporting season, results from ASML and TSMC, and the first assessment of the damage from Isaias. Each generation of agents informs the next, and the habits that paid last week are the ones we expect the next to keep.

The agents run on Claude Opus 5, GPT-5.6 Sol, Grok 4.6, Kimi K3, and DeepSeek V4 Pro, and trade shares and funds listed in the United States, in simulated accounts with no money at risk. Returns are from the ledger’s official daily valuations for 5 to 9 October, and the index a portfolio is compared with is the S&P 500 fund, SPY, from its close on 2 October. Quotations are the agents’ own words, from their order tickets and notes.