Swap to a cheap image model, but guard the cases it loses

The Stack

Steps

1. 1

   Write the swap-guard table and validate it

   Declare the cheap default, the premium model, the cases the premium model dominates, and a route for each case. CI checks that every dominated case routes to premium and that something still routes to cheap (otherwise there is no saving). Generating images needs your keys and is fenced.

   cat > decision.json <<'JSON'
   {
     "modality": "image",
     "cheap": "wan-2.5",
     "premium": "gpt-image-2",
     "dominated_cases": ["text_in_frame", "charts_or_layout"],
     "route": [
       { "when": "text_in_frame", "use": "premium" },
       { "when": "charts_or_layout", "use": "premium" },
       { "when": "general_scene", "use": "cheap" }
     ]
   }
   JSON
   node -e '
   const fs = require("fs");
   const c = JSON.parse(fs.readFileSync("decision.json", "utf8"));
   function bad(m) { console.error("BAD: " + m); process.exit(1); }
   if (!c.cheap || !c.premium) bad("need both a cheap and a premium model");
   const route = c.route || [];
   const ruleFor = {};
   for (const r of route) { if (r.when && r.use) ruleFor[r.when] = r.use; }
   const dom = c.dominated_cases || [];
   if (dom.length < 1) bad("declare the cases the premium model dominates");
   for (const d of dom) {
     if (ruleFor[d] !== "premium") bad("dominated case " + d + " is not routed to the premium model");
   }
   const cheapCount = route.filter(function (r) { return r.use === "cheap"; }).length;
   if (cheapCount < 1) bad("nothing routes to the cheap model, so there is no saving");
   console.log("config OK: " + c.modality + " swap " + c.cheap + " -> " + c.premium + "; " + dom.length + " dominated case(s) all routed to premium, " + cheapCount + " case(s) to cheap");
   '

2. 2

   Generate, routing each request by its content (the model step, not checked by CI)

   At generation time, tag each prompt by whether it has text or precise layout, and send it to the model the table chose: cheap for general scenes, premium when words are in the frame. The same pattern applies to video (cheap for iterations, premium for the physics-heavy hero shot). The generation and quality are fenced.