Pick Claude Fable 5 for the hardest reasoning and most complex problems or long-horizon, multi-step agentic work. Pick GPT-5.1 for adaptive reasoning that scales compute to task difficulty or general-purpose reasoning, coding and tool use. On a tight budget at scale, GPT-5.1 is the value pick.
Claude Fable 5 (Anthropic) and GPT-5.1 (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Fable 5 is anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive. GPT-5.1 is openAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences
Price: GPT-5.1 is about 8× cheaper on input ($1.25/$10 per 1M tokens vs $10/$50 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
Context window: Claude Fable 5 holds 2.5× more — 1M (~1,500 pages) vs 400K (~600 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
Recency: Claude Fable 5 is the newer model by about 7 months (released June 9, 2026), usually meaning fresher training data and capabilities.
Specifications
Spec
Claude Fable 5
GPT-5.1
Provider
Anthropic (US)
OpenAI (US)
Released
June 9, 2026
November 13, 2025
Context window
1M (~1,500 pages)
400K (~600 pages)
Price (in/out)
$10/$50 per 1M tokens
$1.25/$10 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text, image, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
The hardest reasoning and most complex problems: Claude Fable 5 — Anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive — and it carries the larger 1M context.
Long-horizon, multi-step agentic work: Claude Fable 5 — Its 1M window holds about 2.5× more than GPT-5.1's 400K in a single prompt.
Frontier-level analysis and research: Claude Fable 5 — Anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive — and it is the newer of the two.
Adaptive reasoning that scales compute to task difficulty: GPT-5.1 — At $1.25/$10 per 1M tokens it undercuts Claude Fable 5 ($10/$50 per 1M tokens), and that gap compounds at volume.
General-purpose reasoning, coding and tool use: GPT-5.1 — OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line — and it runs cheaper at $1.25/$10 per 1M tokens.
A large ~400K context for long documents and sessions: GPT-5.1 — GPT-5.1 lists a large ~400K context for long documents and sessions among its strengths; Claude Fable 5 does not.
Lowest cost at scale: GPT-5.1 — At $1.25/$10 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input: Claude Fable 5 — Its 1M window is about 2.5× larger than GPT-5.1's 400K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume: GPT-5.1 — At $1.25/$10 per 1M tokens it undercuts Claude Fable 5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases: Claude Fable 5 — Larger 1M window fits more in one prompt.
Anyone whose priority is the hardest reasoning and most complex problems: Claude Fable 5 — It is specifically built for that.
Anyone whose priority is adaptive reasoning that scales compute to task difficulty: GPT-5.1 — That is its strongest area.
Claude Fable 5: where it fits
Anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive. Released June 9, 2026 by Anthropic, it is built for the hardest reasoning and most complex problems, long-horizon, multi-step agentic work, frontier-level analysis and research, and work where maximum capability outweighs cost.
Its trade-offs are real: highest price in the Claude lineup, and tier access was temporarily suspended in June 2026 under a US export-control directive. At $10 in / $50 out per million tokens, it sits in the premium price band.
GPT-5.1: where it fits
OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. Released November 13, 2025 by OpenAI, it is built for adaptive reasoning that scales compute to task difficulty, general-purpose reasoning, coding and tool use, a large ~400K context for long documents and sessions, and text and image input.
Its trade-offs: superseded by GPT-5.2 through GPT-5.6 — kept for compatibility rather than being current, no reliably published SWE-Bench Verified figure, exact context window unconfirmed (400K vs 410K across trackers), and premium output price at $10/1M for a now-older model. At $1.25 in / $10 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Claude Fable 5 and GPT-5.1 overlap enough that the right pick depends on your specific job. GPT-5.1 costs less per token; Claude Fable 5 holds the larger context; and each leads in its own area — Claude Fable 5 for the hardest reasoning and most complex problems, GPT-5.1 for adaptive reasoning that scales compute to task difficulty. Rather than crowning one, run the same hard task through both once and let the results decide.
Frequently asked questions
Is Claude Fable 5 or GPT-5.1 better for coding?
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, Claude Fable 5 leans toward the hardest reasoning and most complex problems while GPT-5.1 leans toward adaptive reasoning that scales compute to task difficulty, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Fable 5 or GPT-5.1?
GPT-5.1 is cheaper — $10/$50 per 1M tokens vs $1.25/$10 per 1M tokens, roughly 8× apart on input.
Which has the bigger context window?
Claude Fable 5 — 1M vs 400K, about 2.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Claude Fable 5 and GPT-5.1 together?
Yes — a multi-model platform like LumiChats gives you Claude Fable 5, GPT-5.1 and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, Claude Fable 5 or GPT-5.1?
Claude Fable 5 — released June 9, 2026, about 7 months after GPT-5.1.
Claude Fable 5 vs GPT-5.1
Anthropic · US | OpenAI · US · Updated June 2026
Quick verdict
Pick Claude Fable 5 for the hardest reasoning and most complex problems or long-horizon, multi-step agentic work. Pick GPT-5.1 for adaptive reasoning that scales compute to task difficulty or general-purpose reasoning, coding and tool use. On a tight budget at scale, GPT-5.1 is the value pick.
Claude Fable 5 (Anthropic) and GPT-5.1 (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Fable 5 is anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive. GPT-5.1 is openAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences at a glance
▸Price: GPT-5.1 is about 8× cheaper on input ($1.25/$10 per 1M tokens vs $10/$50 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
▸Context window: Claude Fable 5 holds 2.5× more — 1M (~1,500 pages) vs 400K (~600 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
▸Recency: Claude Fable 5 is the newer model by about 7 months (released June 9, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
Claude Fable 5
GPT-5.1
Provider
Anthropic (US)
OpenAI (US)
Released
June 9, 2026
November 13, 2025
Context window
1M (~1,500 pages)
400K (~600 pages)
Price (in/out)
$10/$50 per 1M tokens
$1.25/$10 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text, image, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
The hardest reasoning and most complex problems
Claude Fable 5
Anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive — and it carries the larger 1M context.
Long-horizon, multi-step agentic work
Claude Fable 5
Its 1M window holds about 2.5× more than GPT-5.1's 400K in a single prompt.
Frontier-level analysis and research
Claude Fable 5
Anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive — and it is the newer of the two.
Adaptive reasoning that scales compute to task difficulty
GPT-5.1
At $1.25/$10 per 1M tokens it undercuts Claude Fable 5 ($10/$50 per 1M tokens), and that gap compounds at volume.
General-purpose reasoning, coding and tool use
GPT-5.1
OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line — and it runs cheaper at $1.25/$10 per 1M tokens.
A large ~400K context for long documents and sessions
GPT-5.1
GPT-5.1 lists a large ~400K context for long documents and sessions among its strengths; Claude Fable 5 does not.
Lowest cost at scale
GPT-5.1
At $1.25/$10 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input
Claude Fable 5
Its 1M window is about 2.5× larger than GPT-5.1's 400K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume
→ GPT-5.1
At $1.25/$10 per 1M tokens it undercuts Claude Fable 5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ Claude Fable 5
Larger 1M window fits more in one prompt.
Anyone whose priority is the hardest reasoning and most complex problems
→ Claude Fable 5
It is specifically built for that.
Anyone whose priority is adaptive reasoning that scales compute to task difficulty
→ GPT-5.1
That is its strongest area.
Claude Fable 5: where it fits
Anthropic's top public Mythos-class model and its most capable yet, though tier access was temporarily suspended in June 2026 under a US export-control directive. Released June 9, 2026 by Anthropic, it is built for the hardest reasoning and most complex problems, long-horizon, multi-step agentic work, frontier-level analysis and research, and work where maximum capability outweighs cost.
Its trade-offs are real: highest price in the Claude lineup, and tier access was temporarily suspended in June 2026 under a US export-control directive. At $10 in / $50 out per million tokens, it sits in the premium price band.
GPT-5.1: where it fits
OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. Released November 13, 2025 by OpenAI, it is built for adaptive reasoning that scales compute to task difficulty, general-purpose reasoning, coding and tool use, a large ~400K context for long documents and sessions, and text and image input.
Its trade-offs: superseded by GPT-5.2 through GPT-5.6 — kept for compatibility rather than being current, no reliably published SWE-Bench Verified figure, exact context window unconfirmed (400K vs 410K across trackers), and premium output price at $10/1M for a now-older model. At $1.25 in / $10 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Claude Fable 5 and GPT-5.1 overlap enough that the right pick depends on your specific job. GPT-5.1 costs less per token; Claude Fable 5 holds the larger context; and each leads in its own area — Claude Fable 5 for the hardest reasoning and most complex problems, GPT-5.1 for adaptive reasoning that scales compute to task difficulty. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both Claude Fable 5 and GPT-5.1 without two subscriptions? LumiChats gives you these plus 40+ models under one ₹69/day pass (about $1/day) — draft with one, cross-check with the other.
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, Claude Fable 5 leans toward the hardest reasoning and most complex problems while GPT-5.1 leans toward adaptive reasoning that scales compute to task difficulty, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Fable 5 or GPT-5.1?
GPT-5.1 is cheaper — $10/$50 per 1M tokens vs $1.25/$10 per 1M tokens, roughly 8× apart on input.
Which has the bigger context window?
Claude Fable 5 — 1M vs 400K, about 2.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Claude Fable 5 and GPT-5.1 together?
Yes — a multi-model platform like LumiChats gives you Claude Fable 5, GPT-5.1 and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, Claude Fable 5 or GPT-5.1?
Claude Fable 5 — released June 9, 2026, about 7 months after GPT-5.1.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.