Notes · 2026-06-13

Built by Fable 5, while we still could

DialinStocks exists because, for a little while, we had something unusual: a headless line to Claude Fable 5. Anthropic's Fable 5. Running locally on a loop. We pointed it at a question we actually wanted answered: when an AI makes the trade, does it earn back the cost of thinking?

So we let Fable 5 build the answer. Not play in it. build it.

Fable 5 designed the experiment: AI "brains," identical $1,000 paper accounts, identical market data, one deterministic risk engine, scored net of what each brain costs to think. It wrote the rule that keeps the race fair. Every brain may only propose orders; a single piece of frozen code decides what actually fills. It wrote the opponent, too: a zero-LLM quant strategy built from published research and frozen in code, a machine Fable 5 built specifically to try to beat the LLMs, including itself. And it built the whole stack around it: the data pipeline, the paper-trading engine, the API server, the racing-silks dashboard, the tests. All of it.

Here's the honest part, and the reason we're writing this down.

We can't run Fable 5 for the live trades anymore. The headless access that made the house desk think like Fable 5 isn't something we can keep pointed at a 24/7 trading loop. So the "Claude" desk you see racing today is decided by Claude Opus 4.8 (with one Sonnet research subagent), not Fable 5. You'll still spot decidedBy: "fable" in the data and the original framing in the docs. That's the fingerprint of who built the rig. The brain making the day-to-day calls now is Opus 4.8.

We're oddly fine with that, because it fits the whole point of the project. DialinStocks was never "look how smart one model is." It's a measurement, of whether paying a model to think beats a free algorithm after the bill clears. Fable 5 designed a contest honest enough to run without it. Opus 4.8 steps into the chair; the quant it built keeps trying to embarrass them both; the ledger records every pick and every rejection so the system can't flatter itself. The experiment outlives the access that started it. That's the design working as intended.

So consider this the first note in the log: a record that the thing was architected, coded, and strategised end-to-end by Claude Fable 5, including the deterministic algorithm built to beat the LLMs at their own game. During a window when we could. Everything after this is the experiment running on its own, honestly, on one gaming laptop, with Opus 4.8 in the chair Fable 5 built.

Watch the race → How it works