The 4-layer system that cuts it 50 to 90%, with the copy-paste setup
A researcher recently pointed Codex at a problem computer scientists file under intractable: finding a provably optimal tokenizer. With light human guidance, Codex ran an entire research loop, discovered a family of constraints it named “cycle constraints,” and produced a provably optimal tokenizer for an entire book in about a day. The frontier moved while most teams looked away, and it moved toward one question: how few tokens does the job actually take.
That question is also your invoice. You pay per token, roughly three-quarters of a word each, on the way in and the way out. Most production apps resend the same system prompt, the same tool list, and the same documents on every call, paying full freight thousands of times a day. Prompt caching alone trims repeated input by up to 90% on Claude. Stack the rest of the system and a typical bill drops by half or more, with the output quality held steady.
This is the full system:
▫️ * The 4-layer token model* that maps every dollar you spend to a lever you control, from the prompt to the agent loop
▫️ * Before-and-after prompt rewrites* that cut input tokens 30 to 60% while holding output quality, ready to copy
▫️ * The prompt-caching setup* that delivers Claude’s 90% discount in practice, with the prefix-ordering rule, the cache_control breakpoints, and the hit-rate target
▫️ * The retrieval pattern* that replaces stuffing whole documents with searching for the chunks that matter
▫️ * The agent and tool diet,* including the serialization trick that halves the cost of structured data
▫️ * The worked ROI math* on a realistic agent workload, so you can size your own savings before you touch a line of code
▫️ * The 8 failure modes* that silently erase your savings, each with the fix
▫️ * The 30-day rollout* from measuring your spend to a fully optimized stack
Pair it with the deeper [AI Corner](https://www.the-ai-corner.com/) library (all included in the [premium subscription](https://www.the-ai-corner.com/subscribe?coupon=de1c3205&utm_content=201996947)):
▫️ The [Prompting and Context Engineering library](https://www.the-ai-corner.com/t/prompting-and-context-engineering?r=1krivi) for the patterns underneath every rewrite
▫️ The [AI Tools and Models library](https://www.the-ai-corner.com/t/ai-tools-and-models?r=1krivi) for model rates and routing
▫️ The [AI Agents library](https://www.the-ai-corner.com/t/ai-agents?r=1krivi) for the agent-loop economics
▫️ The [Claude and Anthropic library](https://www.the-ai-corner.com/t/claude-and-anthropic?r=1krivi) for caching mechanics and model choice
▫️ The [Business and Investing library](https://www.the-ai-corner.com/t/business-and-investing?r=1krivi) for where this margin compounds
Related builds worth reading next: the context engineering guide, the 2026 prompt engineering guide, Claude best practices, loop engineering, and the Codex background workflows playbook.
The full system in one place: the 4-layer model, the prompt rewrites, the caching setup, the retrieval pattern, the agent and tool diet, the ROI math, the 8 failure-mode fixes, and the 30-day rollout.
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