Opinion: GPT-6.1 Sol may be the best default model for Codex users
The author examined OpenAI’s Codex model lineup and found that GPT‑6.1 Sol delivers performance close to the top‑tier GPT‑6 Astra while costing about one‑fifth as much in the official benchmarks. OpenAI’s pricing sheet shows GPT‑6.1 Sol’s output price at $10 per million tokens, half the $20 price for GPT‑5.6 Sol and lower than the $12 for GPT‑5.6 Terra. Smaller models such as GPT‑6 Luna cost…
Key points
- GPT‑6.1 Sol matches GPT‑6 Astra on complex benchmarks at roughly one‑fifth the cost
- Output price: $10/1M tokens for 6.1 Sol, $20 for GPT‑5.6 Sol, $0.50 for GPT‑6 Luna
- Credit ratios: Astra ~5×, GPT‑5.6 Sol ~2×, GPT‑5.6 Terra ~1.2×, Luna 1/20× of 6.1 Sol
Because API fees differ from the credit‑based quotas used by ChatGPT Plus and Codex Business plans, the author recommends using the unit‑price ratios as a guide: GPT‑6 Astra consumes about five times the credits of 6.1 Sol, GPT‑5.6 Sol about twice, and GPT‑6 Luna only one‑twentieth. The piece also explains Codex’s “effort” levels, suggesting developers start with the “Medium” setting on 6.1 Sol and only raise it for harder tasks, switching to Astra for problems that cannot be solved otherwise. The overall advice is to balance performance, cost, usage limits, and effort rather than automatically picking the newest model.
Model pages: GPT-6.1 Sol → · GPT-6-Astra → · GPT-6 Luna →
[Codex] You might be losing out on model selection? A story about how GPT-6.1 Sol is so excellent that I started questioning the point of using older models
note.com · 18 October 2026
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