Harness Design Notes

Arithmetic for people who serve models

Short technical notes on LLM inference and agent harness design. Each one works out the maths, states its assumptions, and tells you when the technique is not worth building — or the price not worth paying.

Model architecture

Looped Transformers

Run the same block of layers again and again. Build one, watch it reason hop by hop, then price it: a 3.5B looped model stores like 3.5B and runs like 53B.

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System One models

Four Ways to Not Generate Text

Jev, and the three open models chasing it, answer typed questions without writing a sentence. Race them, then train one in the page and watch it overfit.

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Inference pricing

What Jev's Price Card Implies

TypeSafe AI sells its decision model at a flat rate per input token. That price bounds how big the model can be, and stops covering cost on long documents.

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Inference engines

Speculative Decoding

A small model guesses the next few tokens and the big one checks them in a single pass. 2–3× faster generation, with provably identical output.

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Speculative tool calling · Part 1

The Speculation Ceiling

When an agent writes code that calls tools, you can start the calls before generation finishes. Streaming overlap caps at 2×; running the calls concurrently does not.

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Speculative tool calling · Part 2

Does Speculation Pay?

Part 1 as a calculator. Give it your token rate and tool latency and it says which half, if either, is worth building.

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