Year-long experiment: Claude researches the news before every market open and trades a $1,000 paper portfolio against the S&P 500. Here's Day 1

Most actively managed funds trail the S&P 500 over the long run. So I wanted to see how an AI agent does at the same job, with real research, over a full year, against a scoreboard that can't be argued with. The setup Claude (Sonnet 5.5 at high effort, on a normal Claude Pro plan) manages a $1,000 paper portfolio for 365 trading days. Every weekday before the open it gets its portfolio, a one-line price screen of all 503 S&P 500 stocks, and its own last 10 days of decisions. Its only tools are web search and web fetch: no code, no files. It reads the overnight news and places up to 5 orders. They fill at the opening price, which it can't see when deciding. After the close, the portfolio is valued and compared with $1,000 of SPY bought at the same open and held. The rules (enforced in code, not just in the prompt) Individual S&P 500 stocks only. No ETFs, options, leverage or shorting. Max 5 trades a day and max 30% in any one stock. Orders that break a rule are rejected and logged. Every buy has to be backed by something it read that morning, and it cites its sources. Doing nothing is allowed. Overtrading is the classic way to lose to the index. Day 1 Value Today Change Claude $1,000.79 +0.08% SPY buy & hold $996.57 −0.34% It bought four starter positions and kept 56% in cash: NFLX $100 (−0.1% by the close): down 44% from its high; Deutsche Bank upgraded it to Buy at about 18x 2027 earnings. TMO $120 (+0.5%): Thermo Fisher raised its 2026 guidance; a steady compounder if rising rates hit the market. GOOGL $120 (−0.3%): bought the ~15% pullback on AI-spending worries. XOM $100 (+0.7%): oil above $100 with the Strait of Hormuz shut; also a hedge for the growth names. Kept small because a peace deal could reverse it. Its take on the day: "Stocks fell on Monday … as the 10-year Treasury yield hit 5.23% (highest since 2007), oil stayed above $100, and markets priced roughly a 70% chance of an October Fed hike. I'm holding about 56% in cash while building the portfolio in stages." One day means nothing, of course. I'll post a weekly update with the chart, the trades and Claude's reasoning, including the bad calls. FAQ Real money? No. It's paper trading. Not financial advice, and I don't trade these picks myself. Lookahead? It decides before the open and fills at the open. It never sees a price after its decision. Can I see the prompt and the rules? Yes, ask in the comments. Every decision, source and fill is timestamped in a git log, which I'll publish in full at the end. Prediction time: after 365 trading days, does Claude beat SPY, and by how much?