I swapped Codex to Kimi K3 for a marketing plan. quality gap was smaller than the cost gap

Had to build a 3 month marketing plan from last years campaign data. 40 files scattered around, channel performance, retros, the whole thing. not a chat task but an actual deliverable.

Been running codex as my agent for this kind of work. default is GPT-5.6. wanted to see what happens if you just swap the model and keep everything else fixed. same codex version, same directory, same 40 files, same AGENTS.md and prompt. output spec needed a structured doc with quarterly timeline, channel allocation and budget recs.

Ran 5.6 first then Kimi K3 via CC Switch pointing to Atlas Cloud.

K3 actually read all 40 files without truncating. generated the plan with channel breakdowns and the audience segments were grounded in the source data. token cost was roughly 1/4 of the 5.6 run.

where it needed manual correction. misread two blended ROAS figures as single channel. budget split was way too aggressive on one channel without explaining why. one section referenced a campaign that was paused mid Q3. K3 didnt catch the pause. needed 4 manual edits vs 1 on the 5.6 output.

5.6 took 6 min, 85k tokens, cost $0.74. K3 took 9 min, 92k tokens, cost $0.19.

Quality gap was real but narrow. the cost gap was not. for internal planning drafts where someone reviews the output anyway K3 is def good enough. for anything going straight to a client without a second pass id still use the stronger model or run both and diff them.