CASD: a one-pass prompt optimiser reported to beat GEPA and SkillOpt for about $1.60

A prompt and skill optimisation method called CASD has been doing the rounds this week. It has an off-the-shelf coding agent read a full set of agent logs and write its findings as rules, in a single pass, with no environment access or validation data.

Reported results

• across ALFWorld, two τ²-bench environments and SpreadsheetBench-Verified, one pass averaged +16.6 percentage points, against +10.9 for GEPA and +5.3 for SkillOpt
• about $1.60 per optimised prompt, claimed to be more than 22 times cheaper than validation-gated search
• it beat GEPA on three of four tests and SkillOpt on all four

These figures come from secondary write-ups. We couldn't reach the paper itself, so we can't say who wrote it or when it first appeared, and we aren't presenting it as new.

Why it matters

It fits the pattern of the week: the expensive thing quietly becomes the cheap thing. For anyone running agents, cheap prompt optimisation that needs no validation data is a practical lever, if the results hold up.