Claude Fable 5.1 vs GPT-5.6 Luna: pricing and benchmarks
GPT-5.6 Luna is 98% cheaper on input tokens ($0.20 vs $10.00 per 1M). GPT-5.6 Luna is 98% cheaper on output tokens ($1.20 vs $50.00 per 1M). On our document Q&A workload (50,000 questions a month), GPT-5.6 Luna costs $116.00 a month versus $5,500 for Claude Fable 5.1, 98% less. Claude Fable 5.1 scores 164.5 on the Epoch Capabilities Index vs 156.3 for GPT-5.6 Luna.
Prices verified September 14, 2026.
Which should you choose?
Claude Fable 5.1 scores 164.5 on the Epoch Capabilities Index vs 156.3 for GPT-5.6 Luna.
Claude Fable 5.1 scores 90.2% on FrontierMath (Tiers 1–3) vs 82.1% for GPT-5.6 Luna.
GPT-5.6 Luna costs $0.45 per 1M tokens (3:1 input-to-output mix) vs $20.00 for Claude Fable 5.1, 98% less.
A trade-off: Claude Fable 5.1 is 8.2 ECI points more capable but costs 44.4x as much as GPT-5.6 Luna.
Pricing and specs
| Claude Fable 5.1 | GPT-5.6 Luna | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| API model ID | claude-fable-5-1 | gpt-5.6-luna |
| Input / 1M tokens | $10.00 | $0.20 |
| Cached input / 1M tokens | $0.25 | $0.02 |
| Output / 1M tokens | $50.00 | $1.20 |
| Long-context rates | — | $0.40 in / $1.80 out on long-context requests |
| Context window | 1M tokens | 1.05M tokens |
| Max output | 128K tokens | 128K tokens |
| Batch discount | 50% off | 50% off |
Benchmarks
| Claude Fable 5.1 | GPT-5.6 Luna | |
|---|---|---|
| Epoch Capabilities Index | 164.5 | 156.3 |
| GPQA Diamond· Science reasoning | — | 88.8% |
| FrontierMath (Tiers 1–3)· Advanced math | 90.2% | 82.1% |
| SimpleQA Verified· Factual accuracy | 70.8% | 41.0% |
| ARC-AGI-2· Abstract reasoning | 90.0% | 59.5% |
| DeepSWE· Coding | — | 67.2% |
| APEX-Agents· Agentic work | 47.4% | — |
Source: Epoch AI, best recorded result per model (CC BY 4.0). A dash means no published score. See all benchmarks
Monthly cost for real workloads
| Workload | Claude Fable 5.1 | GPT-5.6 Luna | Difference |
|---|---|---|---|
Support chatbot 100,000 replies a month, ~1,500 input tokens (system prompt + history) and ~400 output tokens each. | $3,500 | $78.00 | GPT-5.6 Luna 98% cheaper |
Document Q&A (RAG) 50,000 questions a month with ~8,000 tokens of retrieved context and ~600 output tokens each. | $5,500 | $116.00 | GPT-5.6 Luna 98% cheaper |
Coding agent 10,000 agent steps a month, ~40,000 input tokens each (70% read from the prompt cache) and ~2,000 output tokens. | $2,270 | $53.60 | GPT-5.6 Luna 98% cheaper |
Estimates use standard list prices and ignore cache-write surcharges. Different tokenizers can count the same text differently, so test with your own prompts.
Claude Fable 5.1 vs GPT-5.6 Luna cost calculator
- $116.00/mo$0.0023 / request
- Claude Fable 5.1Anthropic$5,500/mo$0.11 / request
Standard-tier list prices. Long-context rates apply automatically where the provider publishes a threshold. Excludes cache-write surcharges, taxes, batch and volume discounts.
Claude Fable 5.1 pricing notes
Anthropic’s model for demanding reasoning and long-horizon agentic work.
- Cache hits cost 2.5% of the base input price, versus 10% on other Claude models.
- Cache writes cost $12.50 (5-minute cache) or $20 (1-hour cache) per 1M tokens.
- Uses Anthropic’s newer tokenizer, which produces roughly 30% more tokens for the same text.
- US-only inference (inference_geo: "us") costs 1.1x.
GPT-5.6 Luna pricing notes
The GPT-5.6 model optimized for cost-sensitive, high-volume workloads.
- Cache writes are billed at $0.25 per 1M tokens.
- Fast mode costs 2x the standard rate; Flex costs half.
Frequently asked questions
- Is Claude Fable 5.1 cheaper than GPT-5.6 Luna?
- GPT-5.6 Luna is 98% cheaper on input tokens ($0.20 vs $10.00 per 1M). GPT-5.6 Luna is 98% cheaper on output tokens ($1.20 vs $50.00 per 1M). On our document Q&A workload (50,000 questions a month), GPT-5.6 Luna costs $116.00 a month versus $5,500 for Claude Fable 5.1, 98% less.
- Which is more capable, Claude Fable 5.1 or GPT-5.6 Luna?
- Claude Fable 5.1 scores 164.5 on the Epoch Capabilities Index vs 156.3 for GPT-5.6 Luna.
- How much does Claude Fable 5.1 cost per 1M tokens?
- Claude Fable 5.1 costs $10.00 per 1M input tokens and $50.00 per 1M output tokens, and $0.25 per 1M cached input tokens on Anthropic’s standard tier.
- How much does GPT-5.6 Luna cost per 1M tokens?
- GPT-5.6 Luna costs $0.20 per 1M input tokens and $1.20 per 1M output tokens, and $0.02 per 1M cached input tokens on OpenAI’s standard tier.
- Which has the larger context window, Claude Fable 5.1 or GPT-5.6 Luna?
- GPT-5.6 Luna has the larger context window: 1.05M tokens versus 1M for Claude Fable 5.1.