Prices → Compare → GPT-5.6 Luna vs GPT-5.3 Codex
GPT-5.6 Luna vs GPT-5.3 Codex: API cost compared
GPT-5.6 Luna lists at $0.100 in / $0.600 out per 1M tokens. GPT-5.3 Codex lists at $1.750 in / $14.00. Sticker price only tells you so much — below is what each actually costs across eight production workloads.
Side by side
| GPT-5.6 Luna | GPT-5.3 Codex | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Input per 1M | $0.100 | $1.750 |
| Output per 1M | $0.600 | $14.00 |
| Cached input per 1M | $0.010 | $0.175 |
| Context window | 400k | 400k |
| Blended per 1M (3:1) | $0.225 | $4.812 |
Monthly cost by workload
Caching applied at each workload's typical hit rate. This is where the two models actually separate.
| Workload | GPT-5.6 Luna | GPT-5.3 Codex | Cheaper | Difference |
|---|---|---|---|---|
| Customer support chatbot | $14.64 | $317.45 | GPT-5.6 Luna | $302.81 (95%) |
| RAG document Q&A | $19.60 | $385.00 | GPT-5.6 Luna | $365.40 (95%) |
| Coding agent | $10.45 | $224.88 | GPT-5.6 Luna | $214.43 (95%) |
| Bulk summarization | $138.60 | $2,566 | GPT-5.6 Luna | $2,427 (95%) |
| Structured data extraction | $187.00 | $3,710 | GPT-5.6 Luna | $3,523 (95%) |
| Long-form content generation | $25.46 | $585.55 | GPT-5.6 Luna | $560.09 (96%) |
| Email triage agent | $43.25 | $861.87 | GPT-5.6 Luna | $818.62 (95%) |
| Translation pipeline | $164.47 | $3,718 | GPT-5.6 Luna | $3,554 (96%) |
How to read this
GPT-5.6 Luna is cheaper on the majority of these workloads, but "majority" is not the decision. The output:input price ratio is 6.0 for GPT-5.6 Luna and 8.0 for GPT-5.3 Codex. If your traffic is output-heavy — long-form drafting, translation — the model with the lower output price wins regardless of what the input price suggests. If you are input-heavy — RAG, bulk summarization, agents re-reading a codebase — the cached input rate matters more than either headline number.
Cost is also not the only axis. This site does not benchmark quality, latency, or rate limits, and a model that is 3x cheaper but needs two attempts per task is not cheaper. Use these numbers to size a bill, then validate on your own evals.
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| Model | In /1M | Out /1M | Monthly | vs best |
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