Claude Fable 5 vs GPT-5.5: Which Frontier Model Wins?
Last updated: June 11, 2026. Information current as of: June 11, 2026. Benchmark figures, pricing, availability, rate limits, and leaderboard positions can change quickly; every figure below is linked to the source used.
Disclosure: Benchmark figures are sourced from the linked official announcements, documentation, and independent leaderboards. Company-reported results are labeled as such. Independent results are labeled as independent. Where a number was not publicly disclosed, or not available in comparable form, this article says so.
TL;DR Verdict
- Best overall frontier score: Claude Fable 5 currently leads the independent Artificial Analysis Intelligence Index at 64.9, about five points ahead of GPT-5.5.
- Best API value: GPT-5.5 is cheaper at $5 input / $30 output per million tokens, versus Claude Fable 5 at $10 input / $50 output per million tokens.
- Best coding signal: Claude Fable 5 leads LMArena Code Arena with 1665 +20/-20, while GPT-5.5 xhigh is listed at 1501 +9/-9. OpenAI reports GPT-5.5 at 82.7% on Terminal-Bench 2.0 and 58.6% on SWE-Bench Pro.
- Best consumer ecosystem: GPT-5.5 has the broader ChatGPT/Codex distribution, including ChatGPT, Codex, plugins, tools, and business workspaces.
- Best long-context parity: both models offer roughly million-token-class context: Claude Fable 5 has a 1M-token context window; GPT-5.5 has a 1,050,000-token context window.
- Biggest caveat for Claude: Claude Fable 5 requires 30-day data retention and is not available under zero data retention.
- Biggest caveat for GPT-5.5: GPT-5.5 looks cheaper and very capable, but OpenAI’s strongest published comparison data is first-party and often compares against earlier GPT models, Claude Opus 4.7, or Gemini 3.1 Pro, not Claude Fable 5.
Introduction: Why This Comparison Matters Now
OpenAI and Anthropic are no longer only competing on chat quality. GPT-5.5 and Claude Fable 5 are both positioned as models for longer-running work: coding, research, document analysis, computer use, and agentic workflows that keep going after the first answer. That makes a straight “which chatbot writes nicer prose?” comparison too small.
OpenAI announced GPT-5.5 on April 23, 2026, initially rolling it out to ChatGPT and Codex users, with an April 24 update confirming API availability. Anthropic launched Claude Fable 5 on June 9, 2026 as the first widely available Mythos-class model. The timing matters: GPT-5.5 has had more time to appear in external benchmarks, while Claude Fable 5 is newer but already has strong independent leaderboard signals.
If you are choosing a model for product development, coding agents, customer support, research, internal tools, or content workflows, the decision is not just quality. It is also price, retention policy, fallback behavior, model availability, ecosystem tooling, latency, and whether your workload can tolerate safety-triggered rerouting. For broader AI launch tracking, Kingy AI’s AI category archive and Blog archive are useful companion resources.
Model Overview and Positioning
Anthropic describes Claude Fable 5 as its “most capable widely released model” for demanding reasoning and long-horizon agentic work, with API ID claude-fable-5. It sits above Anthropic’s Opus class as a public, safeguarded version of the Mythos-class line. Claude Mythos 5 shares the same underlying capabilities but is restricted to approved customers through Project Glasswing, according to Anthropic’s launch documentation.
OpenAI describes GPT-5.5 as its newest frontier model for complex professional work, with API alias gpt-5.5 and snapshot gpt-5.5-2026-04-23. OpenAI frames it around coding, professional work, research, documents, spreadsheets, tool use, and computer operation.
| Spec | Claude Fable 5 | GPT-5.5 |
|---|---|---|
| Release date | June 9, 2026 | April 23, 2026; API update April 24, 2026 |
| API model string | claude-fable-5 | gpt-5.5; gpt-5.5-2026-04-23 |
| Context window | 1M tokens | 1,050,000 tokens |
| Max output tokens | 128k tokens | 128,000 tokens |
| Knowledge cutoff | Not publicly disclosed for Fable 5 in the docs reviewed; Anthropic lists reliable/training cutoffs for some other models but not Fable 5 in the same table. | Dec. 1, 2025 |
| Modalities | Text and image input; text output | Text and image input; text output; audio/video not supported |
| Reasoning mode | Adaptive thinking always on; effort controls depth | reasoning.effort: none, low, medium, high, xhigh |
| Tooling | Effort, task budgets, memory tool, code execution, tool calling, context editing, compaction, vision | Web search, file search, image generation, code interpreter, hosted shell, apply patch, skills, computer use, MCP, tool search |
| Fine-tuning | Not publicly disclosed as supported for Claude Fable 5 in the docs reviewed. | Not supported |
Key takeaway: the raw context and output limits are close enough that they should not decide the purchase by themselves. The bigger differences are price, retention policy, safety behavior, independent benchmark position, and ecosystem fit.
Benchmarks and Evals
The benchmark story is uneven because the two vendors have not published a single shared, fully comparable table for Claude Fable 5 versus GPT-5.5. Anthropic’s launch page includes a benchmark chart image and qualitative claims, but many exact numbers are not available as accessible text. OpenAI’s GPT-5.5 launch page provides many exact numbers, but most are not against Claude Fable 5 because Fable launched later.
Independent Leaderboards
| Source | Claude Fable 5 | GPT-5.5 | Interpretation |
|---|---|---|---|
| Artificial Analysis Intelligence Index | 64.9, rank #1 | 60 for GPT-5.5 xhigh | Independent composite favors Fable 5 overall. |
| LMArena Text Arena | 1510 +/- 11, rank #1 | 1481 +/- 5 for GPT-5.5-high; 1474 +/- 5 for GPT-5.5 | Human preference text rankings favor Fable 5 on June 10, 2026. |
| LMArena Code Arena | 1665 +20/-20, rank #1 | 1501 +9/-9 for GPT-5.5 xhigh codex harness | Frontend/web-dev arena strongly favors Fable 5. |
| LMArena Vision Arena | 1307 +/- 15, rank #2 | 1284 +/- 8 for GPT-5.5-high; 1283 +/- 8 for GPT-5.5 | Fable 5 is ahead, but confidence intervals overlap with nearby top models. |
These are the cleanest public comparison points because both models appear on the same independent leaderboard families. The caveat is that leaderboards are dynamic. Arena rankings depend on vote volume and prompt mix; Artificial Analysis composites depend on their chosen benchmark weights. For an ongoing model watchlist, see Kingy AI’s AI tools directory and AI launches hub .
Coding and Software Engineering
| Eval | Claude Fable 5 | GPT-5.5 | Source type |
|---|---|---|---|
| Terminal-Bench 2.0 | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 82.7% | GPT number is company-reported by OpenAI. |
| SWE-Bench Pro | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 58.6% | Company-reported by OpenAI; OpenAI notes memorization concerns around this eval. |
| Artificial Analysis Coding Index | 62.0 | 59.1 | Secondary display of Artificial Analysis-derived coding index via Requesty; use as directional. |
| Anthropic launch claims | Highest among frontier models on Cognition’s FrontierCode, exact score not disclosed in accessible text. | Not a shared Anthropic row. | Company-reported and customer-reported claims. |
Interpretation: if you need a citeable, numeric Terminal-Bench or SWE-style score today, OpenAI’s GPT-5.5 page is easier to audit. If you care about independent leaderboard position for web-dev and broad coding preference, Claude Fable 5 has the stronger current signal. The conservative conclusion is that both are frontier coding models, with Fable 5 looking stronger in independent arenas and GPT-5.5 looking strong in OpenAI’s own agentic coding suite.
Reasoning, Knowledge, Math, and Professional Work
| Category | Claude Fable 5 | GPT-5.5 |
|---|---|---|
| GPQA Diamond | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 93.6% |
| Humanity’s Last Exam, no tools | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 41.4% |
| Humanity’s Last Exam, with tools | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 52.2% |
| FrontierMath Tier 1-3 | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 51.7% |
| FrontierMath Tier 4 | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 35.4% |
| GDPval wins or ties | Not publicly disclosed in accessible text for Fable 5 in the sources reviewed. | 84.9% |
OpenAI gives more exact figures across academic and professional evals. Anthropic gives stronger high-level positioning and customer evidence for Fable 5 in software engineering, finance, vision, and life sciences, but not the same accessible row-by-row numeric table. The right reading is not “GPT-5.5 wins all academic work”; it is “GPT-5.5 is easier to audit on these particular published benchmark rows.”
Agentic, Tool Use, Long Context, and Vision
| Area | Claude Fable 5 | GPT-5.5 |
|---|---|---|
| Computer use | Anthropic says Fable 5 is built for long-running autonomous work; exact OSWorld number not publicly disclosed in accessible text. | 78.7% on OSWorld-Verified |
| Tool use | Supports tool calling, code execution, memory tool, task budgets, context editing, compaction, and vision. | 84.4% BrowseComp, 75.3% MCP Atlas, 98.0% Tau2-bench Telecom |
| Long context | 1M-token context; independent long-context exact results not found in accessible public text. | 45.4% on Graphwalks BFS 1M F1 and 58.5% on Graphwalks parents 1M F1 |
| Vision | Anthropic says Fable 5 is state of the art for vision tasks; LMArena lists 1307 +/- 15. | OpenAI reports 81.2% on MMMU Pro without tools and 83.2% with tools; LMArena lists 1284 +/- 8 for high. |
Key takeaway: for broad external leaderboard performance, Fable 5 looks like the new leader. For exact company-published benchmark rows, GPT-5.5 is currently easier to cite.
Pricing and Value
| Item | Claude Fable 5 | GPT-5.5 |
|---|---|---|
| Standard API input | $10 / 1M tokens | $5 / 1M tokens |
| Standard API output | $50 / 1M tokens | $30 / 1M tokens |
| Cached input | Prompt-cache price for Fable 5 not confirmed in accessible docs reviewed. | $0.50 / 1M cached input tokens |
| Long-context surcharge | Not found in docs reviewed. | Prompts above 272K input tokens are priced at 2x input and 1.5x output for the full session. |
| Batch/Flex | Not confirmed for Fable 5 in the docs reviewed. | Batch and Flex at half standard API rate. |
For a 100,000-input-token, 5,000-output-token task, Claude Fable 5 costs about $1.25 using its $10/$50 per million token pricing. GPT-5.5 costs about $0.65 using its $5/$30 per million token pricing. For a 50,000-input-token, 10,000-output-token coding-agent run, Fable costs about $1.00 and GPT-5.5 costs about $0.55. For a 600,000-input-token, 20,000-output-token long-document run, Fable costs about $7.00 at standard rates, while GPT-5.5 would be about $6.90 after OpenAI’s above-272K surcharge.
For consumer plans, Claude Fable 5 had a temporary inclusion window: Anthropic said Fable 5 is included on Pro, Max, Team, and seat-based Enterprise plans through June 22, 2026, then requires usage credits unless capacity allows an extension. OpenAI says GPT-5.5 Thinking is available to Plus, Pro, Business, and Enterprise users, and GPT-5.5 Pro is available to Pro, Business, and Enterprise users in ChatGPT; in Codex, GPT-5.5 is available for Plus, Pro, Business, Enterprise, Edu, and Go plans with a 400K context window.
Value verdict: GPT-5.5 is the default value pick for API workloads unless Fable 5’s quality advantage reduces retries enough to offset the higher unit price. For high-stakes coding and research tasks, a higher per-token price can still be rational if it prevents failed runs.
Speed and Latency
Artificial Analysis provider measurements make the latency tradeoff plain. For Claude Fable 5 with max effort and Opus 4.8 fallback, Anthropic is listed at 63.4 output tokens per second with 109.12 seconds time to first token. For GPT-5.5 high, OpenAI is listed at 50.0 output tokens per second with 31.12 seconds time to first answer token. For GPT-5.5 xhigh, OpenAI is listed at 49.7 output tokens per second with 98.57 seconds time to first token.
The plain-English read: GPT-5.5 high is much more interactive than Claude Fable 5 max effort in the Artificial Analysis measurement window, while GPT-5.5 xhigh is closer to Fable-style wait times. Fable’s throughput after it starts can be strong, but the first-token delay matters for chat UX, customer support, and coding loops where the user wants immediate feedback.
Ease of Use and Developer Experience
GPT-5.5 benefits from OpenAI’s all-in ecosystem: Responses API, Chat Completions, Codex, hosted shell, apply patch, computer use, MCP, web search, file search, image generation, and code interpreter support are all listed on the model page. That makes GPT-5.5 the more obvious fit if your product already runs on OpenAI tools.
Claude Fable 5 has a serious developer story too: Anthropic lists effort, task budgets, memory tool, code execution, programmatic tool calling, context editing, compaction, and vision as supported at launch, and provides explicit refusal/fallback handling guidance for Fable 5. The integration catch is that Fable can return a successful HTTP 200 response with stop_reason: “refusal”, so apps need to handle that path.
For migration, GPT-5.5 is easier for OpenAI shops and Claude Fable 5 is easier for existing Claude Code, Claude API, AWS Bedrock, Vertex AI, or Microsoft Foundry users. Kingy AI’s AI coding tools launch category and AI agents launch category can be natural next reads once those slugs are verified.
Consumer Experience
In ChatGPT, GPT-5.5 lives inside a mature consumer workspace: chat, Codex, files, tools, plugins, business apps, canvas-style workflows, data analysis, voice-related products, mobile apps, and team controls. OpenAI says GPT-5.5 is rolling out to Plus, Pro, Business, and Enterprise users, with GPT-5.5 Pro for Pro, Business, and Enterprise.
Claude’s consumer experience is strongest for people who like Claude’s writing style, Artifacts-style creation, Claude Code, projects, large files, and Anthropic’s interface choices. The biggest Fable-specific consumer wrinkle is access duration: Anthropic says Fable 5 is included on paid plans only through June 22, 2026, after which usage credits are required unless capacity allows an extension.
Writing and Creative Quality
There is no clean universal writing benchmark that should decide this comparison. Claude models have a strong reputation among writers and analysts for prose, structure, and nuance, but preference depends heavily on prompt style and desired voice. GPT-5.5’s advantage is often workflow breadth: it can write, research, analyze files, use tools, create documents, and operate across ChatGPT/Codex surfaces. Fable 5’s advantage is its current independent leaderboard strength and Anthropic’s claimed improvements in long-horizon reasoning.
For pure editorial work, choose the model whose drafts need fewer human edits in your house style. For research-heavy content systems, run a small bake-off: same brief, same source pack, same target audience, same fact-check pass. Tie the winner to production edit time, not vibes.
Safety, Alignment, and Enterprise Readiness
OpenAI says GPT-5.5 went through its full predeployment safety evaluations, Preparedness Framework work, targeted red-teaming for cyber and biology capabilities, and feedback from nearly 200 early-access partners. OpenAI also says business data is not used for training by default and lists compliance alignment including CSA STAR, SOC 2 Type 2, and ISO/IEC 27001, 27017, 27018, and 27701.
Anthropic’s Fable safety design is more visible in the product behavior. Fable 5 includes safety classifiers that can decline requests, with fallback pathways documented for developers. The major enterprise caveat is data retention: Anthropic states that Claude Fable 5 and Claude Mythos 5 are Covered Models with 30-day data retention required, and that zero data retention is not available for those models. Anthropic’s trust materials list compliance artifacts through the Anthropic Trust Center and cite certifications including ISO 27001, ISO/IEC 42001, SOC 2 Type I, and SOC 2 Type II.
Enterprise verdict: GPT-5.5 is easier to approve where zero data retention or standard OpenAI enterprise controls are already in place. Claude Fable 5 may be compelling for capability, but the 30-day retention requirement is a real procurement and compliance gate.
Real-World Use-Case Recommendations
| Use case | Recommended model | Why |
|---|---|---|
| Frontend/web-dev coding agents | Claude Fable 5 | It leads LMArena Code Arena at 1665 +20/-20. |
| Cost-sensitive API workloads | GPT-5.5 | Lower standard token prices: $5/$30 versus Fable’s $10/$50. |
| Strict zero data retention | GPT-5.5, subject to OpenAI contract | Fable 5 explicitly requires 30-day retention. |
| Long-context document reasoning | Test both | Both have million-token-class context; GPT has more exact published long-context eval rows, while Fable has strong independent leaderboard position. |
| ChatGPT/Codex-native teams | GPT-5.5 | It is deeply wired into ChatGPT and Codex surfaces. |
| Claude Code-heavy teams | Claude Fable 5 | Claude shops benefit from native effort, task budget, memory, tool calling, and Claude Code workflows. |
| Customer support agents | GPT-5.5 first; test Fable | OpenAI reports 98.0% on Tau2-bench Telecom; Fable requires refusal/fallback handling. |
| Regulated industries | Depends on retention policy | Fable capability may be attractive, but retention and fallback requirements must clear governance. |
Community and Expert Reception
Reception is split in a predictable way. Independent leaderboards and early customers make Fable 5 look like a step-change model, especially for coding, vision, and long-horizon work. Anthropic’s own customer quotes cite major coding, finance, legal, and research improvements, but those are selected testimonials and should not be treated as neutral evidence.
GPT-5.5, meanwhile, has had a month-plus head start in production use. OpenAI’s launch materials emphasize tool use, Codex, workplace tasks, and efficiency. External measurements show GPT-5.5 remains extremely competitive, especially given its lower API cost. The current consensus I would trust is narrow: Fable 5 appears to lead in independent frontier scores right now, while GPT-5.5 is the cheaper and more broadly integrated platform choice.
Limitations and Open Questions
- Claude Fable 5 exact scores for several standard benchmarks were not available in accessible text in the official sources reviewed.
- GPT-5.5’s strongest numeric benchmark table is first-party and largely predates Claude Fable 5.
- Leaderboard rankings can move as votes, prompts, providers, and harnesses change.
- Claude Fable 5’s refusal and fallback behavior can change the effective model used for sensitive workloads.
- Neither vendor discloses parameter counts for these proprietary models in the sources reviewed.
- Real price-performance depends on retries, cache hit rate, reasoning effort, prompt length, and whether outputs need human repair.
Final Verdict
Claude Fable 5 is the capability pick if you want the strongest current independent leaderboard signal and you can accept its price, latency profile, and 30-day data retention requirement. GPT-5.5 is the pragmatic platform pick if you want lower API costs, strong benchmark numbers, mature ChatGPT/Codex distribution, and a broad tool ecosystem.
So the answer is not a forced single winner. For elite coding, vision-heavy work, and maximum frontier capability, start with Claude Fable 5. For production APIs, cost-sensitive workloads, ChatGPT/Codex workflows, and enterprise environments with existing OpenAI controls, start with GPT-5.5. Serious teams should run both against the same private task set before standardizing. For future comparisons, follow Kingy AI’s AI coding tools coverage and AI sponsored video ROI calculator .
FAQ
Is Claude Fable 5 better than GPT-5.5 for coding?
For independent coding preference, Claude Fable 5 currently looks stronger: it leads LMArena Code Arena at 1665 +20/-20. GPT-5.5 still has strong company-reported coding results, including 82.7% on Terminal-Bench 2.0.
Is GPT-5.5 cheaper than Claude Fable 5?
Yes. GPT-5.5 costs $5 input / $30 output per million tokens. Claude Fable 5 costs $10 input / $50 output per million tokens.
Which model has a larger context window?
GPT-5.5 is slightly larger on paper at 1,050,000 tokens. Claude Fable 5 is listed at 1M tokens.
Does Claude Fable 5 support zero data retention?
No. Anthropic states that Claude Fable 5 and Claude Mythos 5 require 30-day data retention and are not available under zero data retention.
Does GPT-5.5 support fine-tuning?
No. OpenAI’s GPT-5.5 model page lists fine-tuning as not supported.
Which model is better for regulated industries?
GPT-5.5 is easier to consider first if zero data retention or existing OpenAI enterprise controls are required. Claude Fable 5 may still be viable, but its 30-day retention requirement needs legal and security review.
Which model is better for writing?
There is no universal winner. Claude often has strong prose preference among users, while GPT-5.5 has a broader productivity ecosystem. Test both against your house style and measure edit time.
Are the benchmark numbers directly comparable?
Only sometimes. Independent leaderboard rows from Artificial Analysis and LMArena are more comparable. First-party benchmark tables often use different test dates, harnesses, competitors, and disclosure formats.
What is Claude Mythos 5?
Anthropic says Claude Mythos 5 shares Claude Fable 5’s capabilities but is restricted to approved customers through Project Glasswing, with different safeguards.
Should I switch from GPT-5.5 to Claude Fable 5?
Switch only if Fable 5 beats GPT-5.5 on your real tasks by enough to justify higher token prices, slower first-token times at high effort, and the retention requirement.
Sources
Official Sources
- Anthropic: Claude Fable 5 and Claude Mythos 5
- Anthropic docs: Models overview
- Anthropic docs: Introducing Claude Fable 5 and Claude Mythos 5
- Anthropic docs: API and data retention
- Anthropic Trust Center resources
- Anthropic certification article
- OpenAI: Introducing GPT-5.5
- OpenAI API docs: GPT-5.5 model page
- OpenAI: GPT-5.5 System Card
- OpenAI business data, privacy, security, and compliance
Independent and Secondary Sources
- Artificial Analysis: Claude Fable 5 launches at #1
- Artificial Analysis: Claude Fable 5 model page
- Artificial Analysis: GPT-5.5 xhigh model page
- Artificial Analysis: Claude Fable 5 provider performance
- Artificial Analysis: GPT-5.5 high provider performance
- Artificial Analysis: GPT-5.5 xhigh provider performance
- LMArena / Arena: Text Arena leaderboard
- LMArena / Arena: Code Arena leaderboard
- LMArena / Arena: Vision Arena leaderboard
- Requesty: Coding model ranking using Artificial Analysis Coding Index
