Chat With Claude Fable 5.1 on Lorka AI

Take frontier coding and advanced research further. Try Claude Fable 5.1 online with Lorka AI for difficult coding, research, computer-use workflows, and much more.

Claude
Ask anything...
Reasoning
💡💡💡💡💡
Frontier Mythos-class
Speed
Medium
Context Handling
🧠🧠🧠🧠🧠
Strong
Input
Text, Image
Output
Text

A Mythos 5.1-class frontier model engineered for the most demanding reasoning, long-horizon agentic work, and advanced coding, now available to the public.

Context window1M tokens
Max output tokens128K tokens
Knowledge cutoffJune 2026

Claude Fable 5.1 Capabilities: Frontier Coding and Research

Take on projects that demand deeper investigation, sustained reasoning, and reliable execution across many steps.

Frontier coding and root-cause analysis

Investigate difficult software failures across repositories, dependencies, logs, and system state, backed by a 73.4% CursorBench 3.2.0 score.

Strong long-running agents

Plan, execute, verify, and revise multi-step coding, research, computer-use, and project workflows across a 1M-token context window.

Advanced knowledge work

Analyze documents, evidence, financial materials, and multi-part professional requests with 1853 Elo on GDPval-AA v2.

Better results at lower effort

Use adjustable effort levels to balance reasoning depth and token use, with typical workload costs reduced by about 25% vs. Fable 5.

More precise safeguards

Work on legitimate technical and research problems with safeguards designed to reduce unnecessary refusals while maintaining restrictions around high-risk activity.

Claude Fable 5.1 Benchmarks: Real Production-Style Workflows

These compact prompt → output examples show how its coding, analysis, and long-horizon strengths translate into practical work.

User

Analyze this crash report and C++ code. Identify the root cause, implement the safest fix, and give me a regression test. std::string get_name(const User* user) { return user->profile->display_name; } // crash SIGSEGV at get_name(User const*) + 0x14 user = 0x7f21... user->profile = 0x0

Claude
Claude Fable 5.1Production crash root-cause analysis

The immediate failure is a null dereference of user->profile. Protecting only user would not resolve it.

JSON
1std::string get_name(const User* user) {
2 if (!user || !user->profile) {
3 return {};
4 }
5 return user->profile->display_name;
6}
7Regression test:
8TEST(GetName, HandlesMissingProfile) {
9 User user{};
10 user.profile = nullptr;
11
12 EXPECT_EQ(get_name(&user), "");
13}

Next, trace where profile becomes optional. If the domain contract requires every persisted user to have one, this guard prevents the crash but does not eliminate the upstream data-integrity defect.

User

Three services still call users-v1. Map the migration to users-v2, identify compatibility risks, and give me a safe first implementation phase.

Claude
Claude Fable 5.1Repository-scale migration planning

gateway └─ POST /checkout └─ orders-service ├─ users-v1 /users/{id} └─ risk-service └─ users-v1 /profiles/{id} “Primary risk: users-v1 returns full_name; users-v2 splits this into given_name and family_name. Introduce an adapter before changing consumers.”

JSON
1export function normalizeUser(v2: UserV2): LegacyUser {
2 return {
3 id: v2.id,
4 full_name: [v2.given_name, v2.family_name]
5 .filter(Boolean)
6 .join(" "),
7 };
8}
9Phase 1 validation:
10npm test -- users-adapter
11npm run contract:test -- users-v2
12npm run integration:test -- checkout

Deploy behind a 5% feature flag, compare response/error metrics against v1, then increase traffic only after contract parity is confirmed.

User

Revenue is $24M, gross margin is 72%, operating expenses are $20M, and revenue is expected to grow 18%. Estimate next-year operating profit if gross margin reaches 74% and OpEx grows 8%.

Claude
Claude Fable 5.1Financial scenario analysis

Next-year revenue = $24.0M × 1.18 = $28.32M Gross profit = $28.32M × 0.74 = $20.9568M Next-year OpEx = $20.0M × 1.08 = $21.60M Operating profit = $20.9568M − $21.60M = −$0.6432M “Under these assumptions, the company remains approximately $643K operating-loss-making. Break-even requires either roughly 76.3% gross margin at the projected revenue level or lower OpEx, assuming the other variables remain fixed.”

User

Review the supplied studies and experiment logs. Separate established findings from assumptions, identify the biggest evidence gap, and propose the next analysis.

Claude
Claude Fable 5.1Research workflow with evidence gaps

ESTABLISHED • Runs A–C show the intervention improves the target metric. • The effect appears in both evaluation datasets. • Run D does not reproduce the full improvement. NOT YET ESTABLISHED • Whether the gain generalizes beyond the tested distributions. • Whether architecture or training-data differences caused Run D. • Whether the observed improvement survives the ablation. NEXT TEST 1. Hold architecture constant. 2. Run baseline and intervention with identical seeds. 3. Repeat across five seeds. 4. Report mean effect and 95% confidence interval. “For measured differences d1...dnd_1...d_n, report: dˉ=1n∑i=1ndi\bar d = \frac{1}{n}\sum_{i=1}^{n}d_i and CI95=dˉ±t0.975,n−1sdnCI_{95} = \bar d \pm t_{0.975,n-1}\frac{s_d}{\sqrt n} This isolates whether the reported improvement persists once run-to-run variance is accounted for.

What Is Claude Mythos 5.1?

Claude Mythos 5.1 is the same underlying model as Claude Fable 5.1, but with specialized safeguards for vetted professionals working in cybersecurity and life sciences.

The same model, with specialized safeguards for vetted professionals.

Mythos 5.1 gives approved cyber defenders and life sciences professionals access to the same core model with safeguards tailored to defensive security and research-and-development work.

It is not a general consumer model and is available only through Anthropic’s trusted-access programs, including the Cyber Verification Program and Life Sciences Verification Program.

For general coding, research, and professional workflows, Claude Fable 5.1 is the broadly available option.


Access Claude Fable 5.1 Along With GPT-6, Gemini 3.8, and More on Lorka AI

Bring frontier models and demanding projects into one workspace so you can choose the right intelligence for each stage of the job.

Compare frontier models in one workspace

Test Claude Fable 5.1 against other leading models such as GPT-6 Astra, Opus 5, Grok 4.6, and more in the same chat.

Match model capability to workload

Reserve high-end reasoning for difficult coding, research, and multi-step analysis while choosing faster models for routine work.

Keep deep-work context together

Organize prompts, documents, technical notes, screenshots, research, and outputs without fragmenting a project across tools.

Evaluate before standardizing

Compare completeness, code quality, grounding, reasoning, and cost before adopting a model for repeatable workflows.

Create reusable professional workflows

Reuse prompt patterns for debugging, repository analysis, technical research, and more in a single AI chat.

Claude Fable 5.1 Tech Specs: Model Type, Context Window, and More

01

MODEL TYPE / TIER

  • Anthropic frontier model designed for sustained, multi-step professional work
  • Generally available Fable variant, distinct from restricted-access Mythos 5.1
02

PRIMARY USE CASES

  • Agentic coding, debugging, software architecture, research, document analysis, financial analysis, computer use, and complex knowledge work
  • Built around long-horizon workflows requiring planning, verification, reprioritization, and extended execution
03

CONTEXT LENGTH / OUTPUT

  • Up to 1M input tokens
  • Up to 128K output tokens for extensive code, documentation, structured analysis, and other long responses
04

MODALITIES & REASONING

  • Inputs: text, images, and files including PDFs
  • Output: text, including code and structured formats such as JSON
  • Adaptive Thinking with Low, Medium, High, Max, and X-High effort settings
05

PERFORMANCE & ECONOMICS

  • Claude Fable 5 is generally available
  • Claude Mythos 5 shares the same underlying capabilities
  • However, access is limited to vetted organizations through Project Glasswing, which has expanded to approximately 200 partners across more than 15 countries
06

KNOWLEDGE & CONSIDERATIONS

  • Knowledge cutoff: June 2026
  • Premium proprietary model whose higher effort settings can increase token consumption
  • Human verification remains important for high-stakes decisions and final production work

How to Use Anthropic Fable 5.1 as a Software Engineer, Technical Lead, Legal Professional, and More

Root-cause debugging for software engineers

Trace difficult failures across services, dependencies, logs, and source code, then turn the diagnosis into a tested implementation.

ClaudeTry this prompt
"

Trace this failure across every relevant service, identify the root cause, implement the safest fix, and provide regression tests.

"

Architecture and migrations for technical leads

Understand interconnected systems, surface dependencies, and turn complex modernization projects into phased engineering plans.

ClaudeTry this prompt
"

Map this architecture end to end, identify dependency risks, and create a phased migration plan with measurable validation criteria.

"

Long-running workflows for AI builders

Design agentic processes that plan work, use tools, validate intermediate results, recover from errors, and complete multi-step objectives.

ClaudeTry this prompt
"

Design an agent workflow that plans this project, executes each stage with tools, verifies results, and reports unresolved risks.

"

Evidence synthesis for research engineers

Connect papers, experimental results, datasets, and technical notes while separating established evidence from hypotheses that still require testing

ClaudeTry this prompt
"

Review these papers and experiment results, identify the strongest evidence and uncertainties, then propose the highest-value next experiments.

"

Decision analysis for finance and strategy professionals

Work through extensive financial materials, assumptions, calculations, and source evidence before producing a decision-ready recommendation.

ClaudeTry this prompt
"

Analyze these reports, transcripts, and financial data, quantify the material drivers, challenge key assumptions, and recommend the best action.

"

Complex document review for legal professionals

Analyze extensive document sets, track important provisions, distinguish facts from interpretations, and surface issues that require professional judgment.

ClaudeTry this prompt
"

Review these agreements against the stated requirements, identify material inconsistencies and missing provisions, and cite supporting document sections.

"

Cross-functional planning for product leaders

Turn fragmented customer feedback, research, operational data, and team notes into prioritized plans with explicit dependencies and decision points.

ClaudeTry this prompt
"

Synthesize these project notes and customer findings into priorities, owners, dependencies, milestones, risks, and decisions requiring leadership approval.

"

Extended investigations for analysts and power users

Keep large collections of evidence in scope while working through questions that require multiple analytical and verification stages.

ClaudeTry this prompt
"

Investigate this evidence set systematically, test competing explanations, flag unsupported assumptions, and return a concise decision-ready conclusion.

"

Claude Fable 5.1 vs. GPT-6 Astra, Grok 4.6, and Other Models

Compare the Claude Fable 5.1 model vs. GPT-6 Astra, Gemini 3.8, Opus 5, and other frontier models available on Lorka AI’s multi-AI platform.

Legend:
💡Reasoning
Speed
🤖Multimodality
🧠Context
(1: Poor – 5: Very good)
Claude

Claude Fable 5.1

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

Frontier software engineering, long-running agents, complex research, architecture work, and demanding knowledge tasks that require consistent accuracy over time.

OpenAI

GPT-6 Astra

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

Advanced coding, computer-use tasks, million-token project analysis, autonomous agents, technical research, and high-stakes professional problem-solving.

Claude

Claude Opus 5

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

High-end coding, deep reasoning, enterprise analysis, complex decision support, and autonomous workflows spanning many connected steps.

Gemini

Gemini 3.8 Flash

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

Fast long-horizon coding, multimodal document review, visual development, large-scale research, and responsive agent-driven automation.

Grok

Grok 4.6

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

Persistent agents, technical investigations, interactive app building, repository analysis, and multi-step research or knowledge workflows.

Kimi

Kimi K3

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

Large-scale software development, multimodal engineering, systems analysis, interface design, and structured agents working with extensive project context.

MetaAI

Muse Spark 1.3

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

Repository-wide coding, advanced debugging, persistent technical agents, multimodal product building, and tool-driven engineering across varied environments.

Claude

Claude Sonnet 5

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

Business analysis, software development, workflow automation, planning, and everyday technical work that benefits from balanced depth and efficiency.

Z.ai

GLM-5.3

Reasoning
💡💡💡💡💡
Speed
Multimodality
🤖🤖🤖🤖🤖
Context
🧠🧠🧠🧠🧠
Ideal Use Cases

End-to-end software work, workflow automation, major code refactoring, technical agents, and cost-efficient development with capable open-weight AI.

Strengths and Limitations of Anthropic Fable 5.1 and Other Top AI Models

Claude

Claude Fable 5.1

Strengths

Excels at frontier coding, long-running agents, research, computer use, and complex knowledge work.

Limitations

Higher token costs and safety routing can constrain cybersecurity and life-sciences workflows.

Claude

Claude Opus 5

Strengths

Offers near-frontier reasoning, coding, and agentic performance at a lower premium cost.

Limitations

Trails Fable 5.1 on hardest agentic coding, research, computer use, and reasoning.

Gemini

Gemini 3.8 Flash

Strengths

Combines fast long-horizon coding, autonomous agents, multimodal input, and competitive introductory pricing.

Limitations

Difficult prompts can consume more reasoning steps and tokens than simpler workloads.

OpenAI

GPT-5.6 Sol

Strengths

Excels at deep reasoning, advanced coding, and specialized scientific or defensive cybersecurity workflows.

Limitations

Tighter safeguards and restricted access can reduce flexibility across broader professional workflows.

Grok

Grok 4.6

Strengths

Combines long-running agents, coding, technical research, interactive product work, speed, and tool use.

Limitations

Its 500K-token context is smaller, and outputs remain text rather than native visuals.

Kimi

Kimi K3

Strengths

Combines 1M context, multimodal input, structured output, and strong long-horizon agentic coding.

Limitations

Its ecosystem and global developer adoption remain less mature than leading American platforms.

MetaAI

Muse Spark 1.3

Strengths

Improves coding, long-horizon execution, complex instruction following, multitasking, and tool-use efficiency for agents.

Limitations

Proprietary access, unavailable maximum reasoning, and unreleased open weights limit deployment flexibility.

Z.ai

GLM-5.3

Strengths

Supports complex coding, structured outputs, agentic technical work, and cost-conscious long-context development.

Limitations

Text-only operation can require more technical integration than fully managed multimodal alternatives.

How to Try Claude Fable 5.1 on Lorka AI

Access Claude Fable 5.1 on Lorka AI’s platform and use it with other AI models like Opus 5, Gemini 3.8, and more.

1. Select Fable 5.1 in the AI chat

Open the model dropdown in the AI chat and select Fable 5.1 to begin your workflow.

2. Enter your prompt

Write a detailed prompt and attach files, screenshots, or documents to provide more context.

3. Get your output

Receive your output and use other AI models in the same chat for a dynamic workflow.

Try Claude Fable 5.1 Now

Create your account on Lorka AI in minutes and begin your workflow with Fable 5.1.

Claude Fable 5.1 FAQs

You can access the Anthropic model through Anthropic’s API, Claude platforms, AWS, Google Cloud, Microsoft Azure, or by selecting it directly from the model list on Lorka AI, which you can combine with top AI models for a dynamic workflow.