GPT-5.6 Luna or Claude Fable 5.1?
Choose GPT-5.6 Luna when high-volume extraction, classification and routine agent tasks is the closer match. Choose Claude Fable 5.1 when ambitious coding, research and long-running asynchronous projects matters more. Test both on the same real tasks before moving a production workflow.
High-volume extraction, classification and routine agent tasks
Ambitious coding, research and long-running asynchronous projects
GPT-5.6 Luna
GPT-5.6 model optimized for cost-sensitive, high-volume workloads.
Official specification ↗Claude Fable 5.1
Anthropic's frontier model for demanding reasoning and long-horizon agentic work.
Official specification ↗Side-by-side comparison
| Category | GPT-5.6 Luna | Claude Fable 5.1 |
|---|---|---|
| Provider | OpenAI | Anthropic |
| Type | Model · Reasoning model | Model · Frontier reasoning model |
| Pricing summary | $0.20 input, $0.02 cached input and $1.20 output per 1M tokens | $10 input, $0.25 cache read and $50 output per 1M tokens |
| Input price | $0.20 / 1M tokens | $10 / 1M tokens |
| Cached input | $0.02 / 1M tokens | $0.25 / 1M tokens |
| Output price | $1.20 / 1M tokens | $50 / 1M tokens |
| Context window | 1.05M tokens | 1M tokens |
| Maximum output | 128K tokens | 128K tokens |
| Knowledge cutoff | February 16, 2026 | June 2026 |
| Reasoning | none, low, medium, high, xhigh, max | Adaptive, always on; high default effort |
| Relative speed | Fast / cost optimized | Slower |
| Input modalities | Text and image | Text and image |
| Output modalities | Text | Text |
| Tools and integrations | Functions, web search, file search, computer use and supported Responses API tools | Claude API tool use, computer use and agent workflows |
| API / access | v1/responses, v1/chat/completions and v1/batch | Claude Messages API |
| Best fit | High-volume extraction, classification and routine agent tasks | Ambitious coding, research and long-running asynchronous projects |
| Company | OpenAI | Anthropic |
| Product category | Model · Reasoning model | Model · Frontier reasoning model |
| Current pricing note | $0.20 input, $0.02 cached input and $1.20 output per 1M tokens | $10 input, $0.25 cache read and $50 output per 1M tokens |
| Best suited to | High-volume extraction, classification and routine agent tasks | Ambitious coding, research and long-running asynchronous projects |
| Key capabilities | 1.05M context; 128K maximum output; Vision input; Responses API tools | Long-horizon agents; Repository-scale coding; Multistep research; Vision and document work |
| Last verified | 2026-09-08 | 2026-09-08 |
| Official product source | https://developers.openai.com/api/docs/models/gpt-5.6-luna | https://platform.claude.com/docs/en/models/fable-5-1/overview |
How we reached this verdict
We looked at the things that affect everyday use: what each product can do, how its plans are structured, where it fits into your existing workflow, and what the provider currently documents. Benchmark results are useful context, but they are not a universal winner score because test settings and tools vary.
Common questions
GPT-5.6 Luna or Claude Fable 5.1: which should I choose?
Choose GPT-5.6 Luna for high-volume extraction, classification and routine agent tasks. Choose Claude Fable 5.1 for ambitious coding, research and long-running asynchronous projects. Validate the decision with your own prompts and total task cost.
Is GPT-5.6 Luna cheaper than Claude Fable 5.1?
Pricing units can differ. GPT-5.6 Luna: $0.20 input, $0.02 cached input and $1.20 output per 1M tokens. Claude Fable 5.1: $10 input, $0.25 cache read and $50 output per 1M tokens. Check tool charges, plan limits, caching and long-context rules before comparing totals.
Which is better for coding and agent work?
Capability depends on the selected product surface, tools and harness. GPT-5.6 Luna is positioned for high-volume extraction, classification and routine agent tasks; Claude Fable 5.1 is positioned for ambitious coding, research and long-running asynchronous projects. Run the same repository task on both.
How do their context windows compare?
GPT-5.6 Luna lists 1.05M tokens; Claude Fable 5.1 lists 1M tokens. A larger limit does not by itself guarantee better retrieval or lower cost.
Official sources
Use these provider pages to confirm current features, pricing and availability.
AI tools change quickly. We checked this page on 2026-09-08. Before you subscribe, confirm the latest price, regional availability and usage limits on the provider website.