context window — The maximum amount of text a model can consider at once — its working memory for the current conversation or task.
model routing — Sending each request to a model chosen by the difficulty of the task, rather than using one model for everything.
AI agent — An AI system that doesn't just answer once but works toward a goal in a loop — taking actions, reading the results, and deciding what to do next.
Why it matters
Anyone running multi-model routingSending each request to a model chosen by the difficulty of the task, rather than using one model for everything.Full definition → in an AI agentAn AI system that doesn't just answer once but works toward a goal in a loop — taking actions, reading the results, and deciding what to do next.Full definition → or IDE loop is likely paying a hidden cache-invalidation tax on every switch; this piece puts numbers on it and gives a concrete mitigation — pin the model per session rather than route per turn.
Key quotes
“Claude Sonnet 5 took over a 60,000-token coding session for me mid-way through, and that one turn billed $0.223. The next turn ran on the same model, in the same conversation, and it cost $0.020.”
Adham Khaled
“A cache belongs to one model, so the moment you switch, the model you switched to has to read the whole conversation again, and you pay full price for every token of it.”
Adham Khaled
“A switch costs about five times a warm turn when you're carrying 10,000 tokens, and nearly eight times when you're carrying 60,000.”
Adham Khaled
“Cursor says roughly 60% of its developers pick a single daily-driver model, which prices routine work at frontier rates.”
Adham Khaled
“a router is a bet on a portfolio that moves faster than the bet can be retrained.”
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