Side-by-side technical and economic comparison between OpenAI's GPT-5.6 Luna and Anthropic's Claude Fable 5.1.
| Metric | GPT-5.6 Luna | Claude Fable 5.1 | Advantage |
|---|---|---|---|
| Provider Organization | OpenAI | Anthropic | — |
| Standard Input / 1M | $0.20 | $10.00 | GPT-5.6 Luna (98% lower) |
| Cached Input / 1M | $0.10 | $0.25 | GPT-5.6 Luna lower |
| Output / 1M | $1.20 | $50.00 | GPT-5.6 Luna lower |
| Context Window | 128k | 200k | Claude Fable 5.1 (200k) |
| Max Generation Tokens | 16.4k | 32.8k | Claude Fable 5.1 |
| Tokenizer Family | OpenAI o200k_base (200k vocabulary) | Anthropic Claude BPE (~65k vocabulary) | — |
Opt for GPT-5.6 Luna when your engineering requirements prioritize OpenAI's ecosystem, specific tokenizer efficiencies (Exact BPE (o200k_base)), or when your expected prompt-to-completion ratios favor its $0.2/M input rate.
Opt for Claude Fable 5.1 when looking for Anthropic's tooling integration, specific context window depth (200k tokens), or when output generation volume favors its $50/M rate.