Pick Claude Fable 5 for the hardest reasoning and most complex problems or long-horizon, multi-step agentic work. Pick GPT-5.4 for strong general-purpose default or coding and software engineering. On a tight budget at scale, GPT-5.4 is the value pick.
Claude Fable 5 (Anthropic) and GPT-5.4 (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-5.4 is openAI's 2026 workhorse — unifies Codex and GPT into a strong default that costs half of GPT-5.5. Their biggest split is price, and the breakdown below shows exactly how that plays out for your workload.
Key differences
Price: GPT-5.4 is about 4× cheaper on input ($2.5/$15 per 1M tokens vs $10/$50 per 1M tokens) — meaningful once you are processing millions of tokens a month.
Context window: both advertise 1M (~1,500 pages). Tie on paper — test on your own long inputs, since usable recall varies by model.
Recency: Claude Fable 5 is the newer model by about 3 months (released June 9, 2026), usually meaning fresher training data and capabilities.
Specifications
Spec
Claude Fable 5
GPT-5.4
Provider
Anthropic (US)
OpenAI (US)
Released
June 9, 2026
March 5, 2026
Context window
1M (~1,500 pages)
1M (~1,500 pages)
Price (in/out)
$10/$50 per 1M tokens
$2.5/$15 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 — A core design strength of Claude Fable 5.
Long-horizon, multi-step agentic work: Claude Fable 5 — A core design strength of Claude Fable 5.
Frontier-level analysis and research: Claude Fable 5 — A core design strength of Claude Fable 5.
Strong general-purpose default: GPT-5.4 — A core design strength of GPT-5.4.
Coding and software engineering: GPT-5.4 — A core design strength of GPT-5.4.
Document understanding and tool use: GPT-5.4 — A core design strength of GPT-5.4.
Lowest cost at scale: GPT-5.4 — At $2.5/$15 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Which should you pick?
A cost-sensitive startup shipping high volume: GPT-5.4 — At $2.5/$15 per 1M tokens it undercuts Claude Fable 5, and on millions of tokens that margin decides the monthly bill.
Anyone whose priority is the hardest reasoning and most complex problems: Claude Fable 5 — It is specifically built for that.
Anyone whose priority is strong general-purpose default: GPT-5.4 — 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-5.4: where it fits
OpenAI's 2026 workhorse — unifies Codex and GPT into a strong default that costs half of GPT-5.5. Released March 5, 2026 by OpenAI, it is built for strong general-purpose default, coding and software engineering, document understanding and tool use, and 1M context with good token efficiency.
Its trade-offs: topped by GPT-5.5 on the hardest tasks, and pricier than open-weight rivals. At $2.5 in / $15 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Claude Fable 5 and GPT-5.4 overlap enough that the right pick depends on your specific job. GPT-5.4 costs less per token; and each leads in its own area — Claude Fable 5 for the hardest reasoning and most complex problems, GPT-5.4 for strong general-purpose default. 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-5.4 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-5.4 leans toward strong general-purpose default, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Fable 5 or GPT-5.4?
GPT-5.4 is cheaper — $10/$50 per 1M tokens vs $2.5/$15 per 1M tokens, roughly 4× apart on input.
Which has the bigger context window?
Both advertise 1M (~1,500 pages). Remember advertised ≠ usable: recall typically degrades before the ceiling.
Can I use both Claude Fable 5 and GPT-5.4 together?
Yes — a multi-model platform like LumiChats gives you Claude Fable 5, GPT-5.4 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-5.4?
Claude Fable 5 — released June 9, 2026, about 3 months after GPT-5.4.
Claude Fable 5 vs GPT-5.4
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-5.4 for strong general-purpose default or coding and software engineering. On a tight budget at scale, GPT-5.4 is the value pick.
Claude Fable 5 (Anthropic) and GPT-5.4 (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-5.4 is openAI's 2026 workhorse — unifies Codex and GPT into a strong default that costs half of GPT-5.5. Their biggest split is price, and the breakdown below shows exactly how that plays out for your workload.
Key differences at a glance
▸Price: GPT-5.4 is about 4× cheaper on input ($2.5/$15 per 1M tokens vs $10/$50 per 1M tokens) — meaningful once you are processing millions of tokens a month.
▸Context window: both advertise 1M (~1,500 pages). Tie on paper — test on your own long inputs, since usable recall varies by model.
▸Recency: Claude Fable 5 is the newer model by about 3 months (released June 9, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
Claude Fable 5
GPT-5.4
Provider
Anthropic (US)
OpenAI (US)
Released
June 9, 2026
March 5, 2026
Context window
1M (~1,500 pages)
1M (~1,500 pages)
Price (in/out)
$10/$50 per 1M tokens
$2.5/$15 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
A core design strength of Claude Fable 5.
Long-horizon, multi-step agentic work
Claude Fable 5
A core design strength of Claude Fable 5.
Frontier-level analysis and research
Claude Fable 5
A core design strength of Claude Fable 5.
Strong general-purpose default
GPT-5.4
A core design strength of GPT-5.4.
Coding and software engineering
GPT-5.4
A core design strength of GPT-5.4.
Document understanding and tool use
GPT-5.4
A core design strength of GPT-5.4.
Lowest cost at scale
GPT-5.4
At $2.5/$15 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Which should you pick?
A cost-sensitive startup shipping high volume
→ GPT-5.4
At $2.5/$15 per 1M tokens it undercuts Claude Fable 5, and on millions of tokens that margin decides the monthly bill.
Anyone whose priority is the hardest reasoning and most complex problems
→ Claude Fable 5
It is specifically built for that.
Anyone whose priority is strong general-purpose default
→ GPT-5.4
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-5.4: where it fits
OpenAI's 2026 workhorse — unifies Codex and GPT into a strong default that costs half of GPT-5.5. Released March 5, 2026 by OpenAI, it is built for strong general-purpose default, coding and software engineering, document understanding and tool use, and 1M context with good token efficiency.
Its trade-offs: topped by GPT-5.5 on the hardest tasks, and pricier than open-weight rivals. At $2.5 in / $15 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Claude Fable 5 and GPT-5.4 overlap enough that the right pick depends on your specific job. GPT-5.4 costs less per token; and each leads in its own area — Claude Fable 5 for the hardest reasoning and most complex problems, GPT-5.4 for strong general-purpose default. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both Claude Fable 5 and GPT-5.4 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-5.4 leans toward strong general-purpose default, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Fable 5 or GPT-5.4?
GPT-5.4 is cheaper — $10/$50 per 1M tokens vs $2.5/$15 per 1M tokens, roughly 4× apart on input.
Which has the bigger context window?
Both advertise 1M (~1,500 pages). Remember advertised ≠ usable: recall typically degrades before the ceiling.
Can I use both Claude Fable 5 and GPT-5.4 together?
Yes — a multi-model platform like LumiChats gives you Claude Fable 5, GPT-5.4 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-5.4?
Claude Fable 5 — released June 9, 2026, about 3 months after GPT-5.4.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.