AI Tools
Claude Fable 5.1 vs GPT-5.6 Sol: which flagship should you use?
Claude Fable 5.1 vs GPT-5.6 Sol: Fable 5.1 costs $10 per million input and $50 per million output tokens on the Claude API, 2.5 times GPT-5.6 Sol's promotional $4 and $20, yet Anthropic's own September 2026 benchmarks put Fable 5.1 ahead of Sol on every task where both were measured.
What matters
- Claude Fable 5.1 costs $10 per million input and $50 per million output tokens on the API versus GPT-5.6 Sol's promotional $4 and $20, a 2.5x output-token gap, verified on both vendors' official pricing pages September 3, 2026.
- The cache-read price inverts the comparison: Fable 5.1 charges $0.25 per million cached tokens, 37.5% under Sol's $0.40, which favors long agent sessions that reuse context.
- Anthropic's launch table, self-reported with production safeguards enabled, puts Fable 5.1 ahead of GPT-5.6 Sol on Terminal-Bench-Science 0.1 (52.6% vs 22.4%), CursorBench 3.2.0 (73.4% vs 67.2%), and GDPval-AA v2 (1,853 vs 1,711); OpenAI has published no counter-benchmarks.
- Claude Pro subscribers get no Fable 5.1 quota: it bills through pay-as-you-go usage credits at API rates, while Max plans include it up to 50% of weekly limits, per Anthropic's support article.
- GPT-5.6 Sol's $4/$20 rate is promotional, guaranteed at least through November 21, 2026, and its model documentation lists a 1,050,000-token context window and 128,000 max output tokens.
What are Claude Fable 5.1 and GPT-5.6 Sol?
Claude Fable 5.1 is Anthropic's flagship model for coding, knowledge work, and long-running agent tasks, announced September 2, 2026. Anthropic's pricing page positions it as the next generation of intelligence for long-running agents, and Anthropic's model documentation recommends Fable 5.1 for demanding reasoning and long-horizon agentic work. Developers call it as claude-fable-5-1 on the Claude API, and it is available today on Amazon Web Services, Google Cloud, and Microsoft Azure. Fable 5.1 defaults to High effort in Claude Code and to Medium in Claude Cowork and on Claude.ai, per the announcement.
GPT-5.6 Sol is OpenAI's flagship model in the GPT-5.6 family, and the gpt-5.6 alias routes requests to it, per OpenAI's model documentation. That page lists a 1,050,000-token context window, 128,000 maximum output tokens, a February 16, 2026 knowledge cutoff, and reasoning effort settings from none and low through medium (the default), high, xhigh, and max. GPT-5.6 Terra at $2 input and GPT-5.6 Luna at $0.20 input per million tokens price far below Sol, so Sol is the premium member of the family on OpenAI's pricing page.
Claude Fable 5.1 vs GPT-5.6 Sol: pricing compared
Verified on the official pricing pages September 3, 2026: Fable 5.1 costs $10 per million input tokens and $50 per million output tokens, with cache reads at $0.25 and cache writes at $12.50. GPT-5.6 Sol costs $4 per million input and $20 per million output on OpenAI's standard tier, with cache reads at $0.40 and cache writes at $5.00. Output is where the gap is widest: $50 versus $20 is a 2.5x difference per million tokens.
OpenAI's $4/$20 rate is promotional, described on its pricing page as a 20% cut on input and a 33% cut on output, guaranteed at least through November 21, 2026. Fable 5.1's $10/$50 is the standard list rate with no expiry stated, and Anthropic's pricing page offers a 50% batch processing discount instead. Sol requests above 272,000 input tokens bill at 2x input and 1.5x output for the full request, and Sol cache writes bill at 1.25x the uncached input rate, per OpenAI's model documentation. Anthropic publishes no comparable long-context surcharge, but its pricing page also states no context window for Fable 5.1.
Which model wins on Anthropic's benchmark table?
Anthropic's September 2, 2026 launch table is the only published head-to-head between the two models, and every figure in it is Anthropic-reported, measured with production safeguards enabled. The columns compare Fable 5.1, Fable 5, Opus 5, and GPT-5.6 Sol:
- Terminal-Bench-Science 0.1 (agentic scientific research): Fable 5.1 scores 52.6%, GPT-5.6 Sol 22.4%, Fable 5 24.7%, Opus 5 29.0%.
- CursorBench 3.2.0 (agentic coding): Fable 5.1 scores 73.4%, GPT-5.6 Sol 67.2%, Fable 5 70.5%, Opus 5 70.0%.
- GDPval-AA v2 (knowledge work): Fable 5.1 scores 1,853, GPT-5.6 Sol 1,711, Fable 5 1,723, Opus 5 1,824.
Read the table with its own footnotes. GPT-5.6 Sol was not measured on several tasks, including OSWorld 2.0 and Humanity's Last Exam, so the direct comparison covers the rows above only. Anthropic also prints that where its safeguards intervened, Fable 5.1 and Fable 5 scored zero on OSWorld 2.0, and that the Terminal-Bench-Science 0.1 standard error runs 3.5 to 4.5 points per model. OpenAI has published no counter-benchmarks on its documentation pages as of September 3, 2026.
The catches: usage credits, cache reads, and context window
Claude plan billing is the first catch. Anthropic's support article, updated September 3, 2026, confirms Fable 5.1 is a standard part of Max plans and premium Team and Enterprise seats, usable up to 50% of weekly usage limits and drawing those limits down faster than other Claude models. On Pro plans and standard Team and Enterprise seats, Fable 5.1 is not included in plan limits: it runs on pay-as-you-go usage credits billed at standard API rates, and the one-time credit Anthropic issued when Fable 5 moved to usage credits in July 2026 does not apply to Fable 5.1.
Cache reads are the second catch. Fable 5.1 reads cached context at $0.25 per million tokens, 37.5% below Sol's $0.40, which favors agent loops that reuse a large context across many steps. Anthropic says the 75% cache-read cut (from $1.00 on Fable 5) lowers typical workload cost around 25% and highly agentic work up to around 45% versus Fable 5.
Context window is the third. GPT-5.6 Sol ships a documented 1,050,000-token window with a published surcharge above 272,000 tokens; Anthropic's pricing page states no context figure for Fable 5.1, so buyers who need a guaranteed giant window get certainty only on the OpenAI side.
Who should use Claude Fable 5.1 vs GPT-5.6 Sol?
- Choose Claude Fable 5.1 for Claude Code and long-horizon agents: it is Anthropic's newest flagship, defaults to High effort inside Claude Code, and Max subscribers get it inside weekly limits rather than on usage credits.
- Choose Claude Fable 5.1 when you buy through a big cloud: availability today on AWS, Google Cloud, and Azure means one existing invoice and no new procurement.
- Choose GPT-5.6 Sol for token-sensitive API bills: at $4 and $20 per million tokens it costs 60% less than Fable 5.1 on both input and output today, with the rate locked at least through November 21, 2026.
- Choose GPT-5.6 Sol for giant single-call context: its documented 1,050,000-token window and reasoning effort up to max cover document and research jobs that need one large pass.
- Budget the promo either way: Sol's cut has a stated floor of November 21, 2026 and no stated post-promo rate, while Fable 5.1's list price has no stated expiry and no stated guarantee.
No independent third-party benchmark of the pair exists yet, and each vendor measures its own model on its own harness. For production agent work, price both on your real workload: Fable 5.1 wins on reported raw scores and cheap cache reads, Sol wins on sticker token price and documented context.
Limitations both vendors leave out
Anthropic's benchmark advantage is self-reported, measured with production safeguards enabled, and the launch page itself flags zero scores where safeguards intervened plus a 3.5 to 4.5 point standard error on Terminal-Bench-Science 0.1. OpenAI publishes no counter-results. Regulatory overhead applies to Fable 5.1 only: released after August 2, 2026, it carries the invisible watermark required under the EU AI Act Code of Practice that Anthropic signed in July 2026, which Anthropic says has no practical impact on output quality.
On the OpenAI side, the $4/$20 rate is a promotion with a stated floor and no stated ceiling, so budgets built on it expire the day the floor does. Neither vendor lists the other's figures, so any side-by-side spreadsheet depends on two pages with two different formats and two different update rhythms.
At a glance
| Feature | Claude Fable 5.1 | GPT-5.6 Sol |
|---|---|---|
| API model ID | claude-fable-5-1 | gpt-5.6-sol (gpt-5.6 alias) |
| Input per 1M tokens | $10.00 | $4.00 (promotional) |
| Output per 1M tokens | $50.00 | $20.00 (promotional) |
| Cache read per 1M | $0.25 | $0.40 |
| Cache write per 1M | $12.50 | $5.00 |
| Context window | Not stated on pricing page | 1,050,000 tokens |
| Max output tokens | Not stated on pricing page | 128,000 |
| Terminal-Bench-Science 0.1 | 52.6% | 22.4% |
| CursorBench 3.2.0 | 73.4% | 67.2% |
| GDPval-AA v2 | 1,853 | 1,711 |
| Batch discount | 50% off | Not stated on pricing page |
FAQ
Is GPT-5.6 Sol cheaper than Claude Fable 5.1?
Per token, yes. OpenAI's promotional rate is $4 input and $20 output per million tokens versus Fable 5.1's $10 and $50, and Sol cache writes cost $5.00 against $12.50. Two details flip parts of the math: Fable 5.1 reads cache at $0.25 per million tokens, under Sol's $0.40, and Anthropic offers 50% off batch processing. OpenAI's promo rate holds at least through November 21, 2026.
Which model is better for coding and agents: Claude Fable 5.1 or GPT-5.6 Sol?
On Anthropic's self-reported benchmarks, Fable 5.1 leads where both were measured: 73.4% to 67.2% on CursorBench 3.2.0 and 52.6% to 22.4% on Terminal-Bench-Science 0.1, with production safeguards enabled. GPT-5.6 Sol supports reasoning effort up to max, while Fable 5.1 defaults to High effort inside Claude Code. No independent head-to-head exists yet, so test on your own workload before migrating.
How long will GPT-5.6 Sol's $4/$20 pricing last?
OpenAI's pricing page says the promotional pricing is available at least through November 21, 2026, and does not state the rate afterward. Claude Fable 5.1 has no promo window: its $10/$50 pricing is the standard list rate, with a 50% batch processing discount on Anthropic's pricing page.
Related reading
Claude Fable 5.1 vs Mythos 5.1, GPT-5.6 Sol pricing, Codex vs Claude Code, Claude pricing and review