Claude Fable 5 vs GPT-5.6 Sol
Anthropic's and OpenAI's frontier flagships compared across context, price, coding standing, and where you can run them.
Updated August 28, 2026 · Independent comparison — Claude Fable 5, GPT-5.6 Sol are separate products.
Claude Fable 5
Anthropic's most capable widely released model
Claude Fable 5 is Anthropic's most capable widely released model, built for the most demanding reasoning and long-horizon agentic work. It carries a 1M-token context window and up to 128K output tokens, with adaptive thinking always on — you can't disable it, only tune depth through the effort ladder (default high). It is the priciest model in this comparison at $10/$50 per million tokens, roughly twice Opus 5's cost, and it requires a data-retention arrangement rather than zero-data-retention. On some coding and debug requests a security classifier may route work to Opus.
GPT-5.6 Sol
OpenAI's flagship GPT-5.6 reasoning model
GPT-5.6 Sol is the flagship tier of OpenAI's GPT-5.6 family, tuned for the hardest professional, coding, and research work and strong at command-line, multi-step problems. It offers roughly a 1.05M-token context window, 128K max output, and a February 2026 knowledge cutoff. Its current API price is a promotional $4/$20 per million tokens (down from a $5/$30 list rate) held at least through November 21, 2026, and requests whose input exceeds 272K tokens are billed at 2x input / 1.5x output for the whole request ($8/$30). The alias gpt-5.6 resolves to Sol, and it is available in ChatGPT Plus and above.
Bottom line
Anthropic's and OpenAI's frontier flagships compared across context, price, coding standing, and where you can run them. Choose Claude Fable 5 if you want Anthropic's single most capable model and will pay top-tier rates; choose GPT-5.6 Sol if you want frontier-class reasoning at roughly half the input cost and a lower output rate.
Context & Limits
| Feature | Claude Fable 5 | GPT-5.6 Sol |
|---|---|---|
| Context window | 1M (1,000,000 tokens) | ~1.05M (1,050,000 tokens) |
| Max output tokens | 128K | 128K |
| Image / vision input | ✓ | ✓ |
| Knowledge cutoff | Not published | February 2026 |
Pricing (per 1M tokens)
| Feature | Claude Fable 5 | GPT-5.6 Sol |
|---|---|---|
| Input | $10.00 | $4.00 (promo; $5.00 list, through 2026-11-21) |
| Output | $50.00 | $20.00 (promo; $30.00 list) |
| Cached input read | $1.00 (0.1x input) | $0.40 |
| Long-context surcharge | None (flat to 1M) | >272K input: 2x in / 1.5x out for the whole request ($8/$30) |
Coding & Agentic Standing
| Feature | Claude Fable 5 | GPT-5.6 Sol |
|---|---|---|
| Positioning | Anthropic's most capable model for the hardest reasoning and coding | OpenAI's flagship for the hardest professional, coding, and research work |
| Agentic / tool use | Built for long-horizon autonomous runs; thinking always on | Strong at command-line and multi-step coding; adds max/ultra reasoning modes |
| Vendor benchmark suites reported | SWE-bench (Verified / Pro) | SWE-bench Pro, Terminal-Bench, TAU-bench |
| Directly comparable head-to-head score | No shared vendor-published benchmark | No shared vendor-published benchmark |
Access & Openness
| Feature | Claude Fable 5 | GPT-5.6 Sol |
|---|---|---|
| Open weights | ✗ | ✗ |
| Where you can run it | Claude API, Claude apps (Max/Team, Pro credits), Cursor Max Mode, OpenCode Zen, DevPass | ChatGPT Plus and above, OpenAI API |
| Reasoning control | Effort low-max; thinking cannot be disabled | reasoning.effort none-max; higher max/ultra modes |
| Premium speed option | Not published | Fast mode (formerly priority) ~2x output speed |
Speed & Fit
| Feature | Claude Fable 5 | GPT-5.6 Sol |
|---|---|---|
| Speed tier | Highest capability, slowest — single hard turns can run minutes | Flagship reasoning tier (Terra/Luna are the faster, cheaper siblings) |
| Best-fit workload | The hardest reasoning and multi-hour autonomous coding runs | Hard coding, research, and command-line agent work |
| Cost note | Roughly 2x Opus 5's price | Roughly half Fable 5's input price at the promo rate |
The Verdict
Choose Claude Fable 5 if...
- ✓You want Anthropic's single most capable model and will pay top-tier rates
- ✓Your work is the hardest reasoning and multi-hour autonomous agent runs
- ✓You rely on always-on deep thinking that can't be switched off
- ✓You're in the Anthropic ecosystem (Claude apps, Cursor Max Mode, OpenCode Zen, DevPass)
Choose GPT-5.6 Sol if...
- ✓You want frontier-class reasoning at roughly half the input cost and a lower output rate
- ✓You live in ChatGPT Plus or the OpenAI API and want the top GPT-5.6 tier
- ✓You value command-line and multi-step coding strength plus max/ultra reasoning modes
- ✓You want the option to drop down to Terra or Luna for cheaper everyday work in the same family
- ✓Your prompts stay under 272K input tokens, avoiding Sol's long-context surcharge
Frequently Asked Questions
What is the difference between Claude Fable 5 and GPT-5.6 Sol?
Claude Fable 5 is Anthropic's most capable widely released model, built for the most demanding reasoning and long-horizon agentic work. GPT-5.6 Sol is the flagship tier of OpenAI's GPT-5.6 family, tuned for the hardest professional, coding, and research work and strong at command-line, multi-step problems.
How much do Claude Fable 5 and GPT-5.6 Sol cost?
Claude Fable 5: $10.00. GPT-5.6 Sol: $4.00 (promo; $5.00 list, through 2026-11-21). See the pricing table above for full plan details.
Should I choose Claude Fable 5 or GPT-5.6 Sol?
Choose Claude Fable 5 if you want Anthropic's single most capable model and will pay top-tier rates. Choose GPT-5.6 Sol if you want frontier-class reasoning at roughly half the input cost and a lower output rate.
1DevToolRun whichever model wins — from one workspace
Both Claude Fable 5 and GPT-5.6 Sol are closed models you reach through an agent or API. 1DevTool runs Claude Code, Codex, and Gemini CLI side by side in persistent terminals, so you can drive Fable 5 and GPT-5.6 Sol from the same workspace with your own keys or subscriptions — no lock-in to either lab. It adds a built-in HTTP client, 13-engine database client, and embedded browser, all wired into Send-to-AI. One-time $29, no subscription.