Drew Breunig sketched a DSPy model router on Jev in 15 minutes
A prompt-level model picker built in one sitting, with no accuracy or cost numbers attached to it yet.
Drew Breunig posted a model router built with DSPy and Jev that chooses the model from the initial prompt. He says he sketched it out in about 15 minutes, by request, and was surprised at how well it works. That is the whole claim, and he did not attach accuracy, latency or cost figures to it.
Sketched this out in ~15 min, by request, and am surprised at how well it works!
Harrison Chase replied that LangChain already ships this shape as ModelRouterMiddleware, where Jev reads the first message, picks the model, and that model handles the whole run. He then suggested going further, re-picking the model after each tool result with a custom hook, on the grounds that Jev is cheap enough to make that affordable.
jev is cheap enough that you can also re-pick after each tool result with a custom hook
What is actually measured here
Nothing, yet. Neither post includes a routing accuracy number, a per-call price, or a comparison against a fixed single-model baseline. "Surprised at how well it works" is one builder's impression of his own 15 minute sketch, not an eval, and the re-pick-after-every-tool-result pattern is a design suggestion from someone describing what the framework allows rather than a result from a run.
That matters because routing is the one place where a cheap classifier's errors compound in a way that is easy to miss. A mis-picked model does not throw, it just quietly does the task worse or more expensively, and without a baseline you cannot tell the difference between a router that is working and a router that is sending everything to the same model anyway.
For people building on it
The per-run version and the per-tool-result version are different cost profiles. One Jev call at the top of a run is close to free against the cost of the run itself. A call after every tool result scales with the length of the agent loop, which is the part nobody posted a number for.
Jev Router, TypeSafe's own hosted routing product, is a separate thing from hand-rolling a router like this. Theo's benchmark of it, which found it almost 5x slower, is earlier.