GPT-5.6 Luna Pro is $9.8 cheaper per 1M input tokens (98% lower; 50x difference).
API cost decision in 10 seconds
GPT-5.6 Luna Pro vs Claude Fable 5
Pick GPT-5.6 Luna Pro when budget and context both matter.
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Data confirmed:
Prices normalized to USD per 1M tokens
Sample workload: 1M input + 500K output
Budget verdict
Pick GPT-5.6 Luna Pro when budget and context both matter.
On the standard 1M input plus 500K output workload, GPT-5.6 Luna Pro is estimated at $0.8 vs $35 for Claude Fable 5, saving $34.2 (97.7% lower).
Cost-first pickGPT-5.6 Luna Pro
Context-first pickGPT-5.6 Luna Pro
Sample savings$34.297.7%
10x traffic gap$342
GPT-5.6 Luna Pro is cheaper on the standard workload and also has the larger context window. At 10x that traffic, the same price gap is about $342. Use the calculator below to replace the sample workload with your own token volume.
Cost sensitivity
Workload Sensitivity
GPT-5.6 Luna Pro stays cheaper across input-heavy, balanced, and output-heavy sample workloads.
| Workload shape | Token mix | Better pick | GPT-5.6 Luna Pro | Claude Fable 5 |
|---|---|---|---|---|
| Input-heavy / RAG | 5M input + 500K output | GPT-5.6 Luna Pro | $1.6 | $75 |
| Balanced workload | 1M input + 1M output | GPT-5.6 Luna Pro | $1.4 | $60 |
| Output-heavy chatbot | 1M input + 5M output | GPT-5.6 Luna Pro | $6.2 | $260 |
GPT-5.6 Luna Pro is $48.8 cheaper per 1M output tokens (97.6% lower; 41.7x difference).
GPT-5.6 Luna Pro has 50K more context (1.05x larger).
GPT-5.6 Luna Pro is $34.2 cheaper on the standard workload (97.7% lower).
Estimate your workload cost
Your Workload Cost
This estimate uses normalized public API pricing per 1M tokens. It is a planning aid, not a billing quote. Verify provider pricing, limits, and terms before production use.
Quick Decision
GPT-5.6 Luna Pro has the lower input price; GPT-5.6 Luna Pro has the lower output price; GPT-5.6 Luna Pro offers the larger context window. For the 1M input plus 500K output sample, GPT-5.6 Luna Pro is cheaper for the standard workload.
For a 1M input token plus 500K output token workload, the estimated API cost is $0.8 for GPT-5.6 Luna Pro and $35 for Claude Fable 5.
Choose GPT-5.6 Luna Pro when you care most about lower input-token price, lower output-token price, and larger context window.
Choose Claude Fable 5 when its provider, model quality, latency, or availability is more important than the numeric price/context winner.
- On the standard 1M input plus 500K output workload, GPT-5.6 Luna Pro is estimated at $0.8 vs $35 for Claude Fable 5, saving $34.2 (97.7% lower).
- GPT-5.6 Luna Pro is $34.2 cheaper on the standard workload (97.7% lower).
- GPT-5.6 Luna Pro is $9.8 cheaper per 1M input tokens (98% lower; 50x difference).
- GPT-5.6 Luna Pro is $48.8 cheaper per 1M output tokens (97.6% lower; 41.7x difference).
- GPT-5.6 Luna Pro has 50K more context (1.05x larger).
| Feature | GPT-5.6 Luna Pro (OpenAI) | Claude Fable 5 (Anthropic) |
|---|---|---|
| Input Price prompt tokens per 1M | $0.2 | $10 |
| Completion Price per 1M tokens | $1.2 | $50 |
| Sample Workload Cost 1M input + 500K output | $0.8 | $35 |
| Context Window | 1.05M | 1M |
| Release Date |
Use-Case Decision Matrix
| Use case | Better pick | Why |
|---|---|---|
| Budget-constrained production | GPT-5.6 Luna Pro | On the standard 1M input plus 500K output workload, GPT-5.6 Luna Pro is estimated at $0.8 vs $35 for Claude Fable 5, saving $34.2 (97.7% lower). |
| High-volume input processing | GPT-5.6 Luna Pro | Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill. |
| Long responses and chatbots | GPT-5.6 Luna Pro | Lower output-token price matters most when assistants generate many completion tokens. |
| RAG or long-document work | GPT-5.6 Luna Pro | A larger context window leaves more room for retrieved passages, conversation history, or source files. |
Related Alternatives
- gpt-oss-120b (free) can replace GPT-5.6 Luna Pro when lower sample workload cost matters most: $0.
- gpt-oss-20b (free) can replace GPT-5.6 Luna Pro when lower sample workload cost matters most: $0.
- gpt-oss-20b can replace GPT-5.6 Luna Pro when lower sample workload cost matters most: $0.1.
- gpt-oss-120b can replace GPT-5.6 Luna Pro when lower sample workload cost matters most: $0.12.
- Grok 4.20 Multi-Agent offers 2M context with $2.5 sample workload cost.
- Grok 4.20 offers 2M context with $2.5 sample workload cost.
- DeepSeek V4 Flash 0731 offers 1.31M context with $0.17 sample workload cost.
- DeepSeek V4 Flash Latest offers 1.31M context with $0.11 sample workload cost.
- DeepSeek V4 Flash 0731 · DeepSeek · #1
- MiMo-V2.5 · Xiaomi · #2
- Hy3 · Tencent · #3
- Ox Alpha · stealth · #4
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Open Anthropic modelsGPT-5.6 Luna Pro is the same underlying model as [GPT-5.6 Luna](https://openrouter.ai/openai/gpt-5.6-luna), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. Learn more in OpenAI's docs: https://developers.openai.com/api/docs/guides/reasoning#reasoning-mode
Claude Fable 5 is a Mythos-class model from Anthropic, built for autonomous knowledge work and coding. It supports text, image, and file inputs with text output, with reasoning support and...