Claude Mythos 5 Limited Access: What It Is, Who Can Use It, Why It Is Restricted, and How It Differs from Fable 5

Claude Mythos 5 is Anthropic’s limited-access model configuration for organizations conducting approved cybersecurity, biology, and other sensitive research whose requirements exceed the safeguards applied to generally available Claude models.

It is not a hidden consumer subscription, a more expensive version of Claude that becomes available after purchasing additional credits, or a model that ordinary Pro, Max, Team, and Enterprise users can activate from the standard Claude selector.

Anthropic provides Mythos 5 only to approved partners through controlled access programs, with eligibility determined by the organization, proposed use, security practices, and ability to operate within monitoring, retention, authorization, and disclosure requirements.

The model shares its underlying intelligence, context window, output capacity, tools, vision capabilities, and standard API pricing with Claude Fable 5, although Fable applies additional safeguards that may block or reroute sensitive cybersecurity, biology, chemistry, frontier-model-development, and model-distillation requests.

Mythos removes those broad domain classifiers for vetted organizations, allowing approved researchers to investigate advanced vulnerabilities or scientific problems that a generally available model may refuse because the same capabilities could also support attacks, exploitation, or dangerous biological work.

The restriction is therefore based on capability and risk rather than price, because an organization willing to pay the standard model rate still cannot obtain access without Anthropic’s approval and the required operating controls.

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Claude Mythos 5 is a restricted configuration of Anthropic’s highest-capability model.

Claude Mythos 5 was created for tasks that require advanced reasoning, coding, tool use, long-horizon agency, scientific analysis, and security research without the domain-specific classifier layer applied to the generally available Fable configuration.

The model can work across software repositories, scientific literature, technical documentation, visual evidence, complex tools, and long-running projects whose intermediate findings must remain available across many steps.

Its cybersecurity capability is particularly significant because Anthropic reports that the Mythos model line can discover, analyse, and exploit software vulnerabilities at a level exceeding most human security practitioners.

Its scientific capability also extends into biology, chemistry, healthcare, and related fields where the same analytical strength can support beneficial research or lower the expertise required for harmful experimentation.

Mythos should consequently be understood as a general frontier model with unusually sensitive specialist capabilities rather than as a narrow vulnerability scanner or laboratory assistant.

The restricted access model allows Anthropic to provide those capabilities to selected organizations while keeping a safeguarded configuration available for ordinary coding, research, business analysis, and knowledge work.

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The principal characteristics of Claude Mythos 5.

Area	Claude Mythos 5 position
Model type	General-purpose frontier reasoning and agentic model
Sensitive strengths	Cybersecurity, biology, chemistry, scientific research, and advanced coding
Access	Approved organizations only
Public sign-up	Unavailable
Ordinary Claude subscription access	Not included
Context window	1,000,000 tokens
Maximum output	128,000 tokens
Input modalities	Text and images
Output modality	Text
Adaptive thinking	Always active
Standard API price	$10 input and $50 output per million tokens
Zero Data Retention	Unsupported
Minimum retention	Thirty days
Main general-access alternative	Claude Fable 5

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Mythos 5 and Fable 5 use the same underlying model intelligence.

The distinction between Mythos 5 and Fable 5 is not that Mythos possesses a completely separate intelligence architecture while Fable runs a smaller or less capable base model.

Anthropic describes them as two configurations of the same underlying model, with matching context capacity, maximum output, adaptive reasoning, vision support, agent tools, code execution, memory features, and standard token prices.

Fable 5 adds classifiers and routing behaviour designed to identify potentially dangerous cybersecurity, biology, chemistry, model-development, and distillation requests.

When a request crosses a sensitive threshold, Fable may refuse it or reroute it to a less capable Claude model that can provide safer assistance without exposing the complete Mythos-level capability.

Mythos removes the same broad classifier layer for approved partners whose work would otherwise be blocked, while maintaining contractual, monitoring, retention, authorization, and usage-policy controls around the organization.

A general user can therefore receive the same underlying model quality for ordinary writing, analysis, coding, document work, vision, and research through Fable, while access to unrestricted sensitive-domain performance remains controlled.

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Claude Mythos 5 and Claude Fable 5 compared.

Comparison area	Claude Mythos 5	Claude Fable 5
Underlying intelligence	Same model	Same model
Context window	1 million tokens	1 million tokens
Maximum output	128,000 tokens	128,000 tokens
Adaptive thinking	Always on	Always on
Vision and tools	Supported	Supported
Standard API price	$10 input and $50 output per million tokens	$10 input and $50 output per million tokens
Cybersecurity classifier	Not applied in the same general-release form	Applied
Biology and chemistry classifier	Not applied in the same general-release form	Applied
Sensitive-request handling	Governed through vetted access and monitoring	May refuse or reroute the request
Availability	Approved organizations	Generally available under paid-plan and usage conditions
Zero Data Retention	Unavailable	Unavailable for the covered configuration
Priority processing tier	Not currently supported	Supported in eligible configurations

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Limited access is an approval model rather than a premium subscription tier.

Claude Mythos 5 does not appear as an optional upgrade for individual users, regardless of whether they subscribe to Claude Pro, Max, Team, or Enterprise.

A normal API key does not expose the claude-mythos-5 model automatically, while purchasing usage credits does not convert an ordinary account into an approved Mythos workspace.

Enterprise customers may have an account relationship through which access can be discussed, although an Enterprise contract alone does not create entitlement.

Anthropic directs interested organizations to contact their Anthropic, Amazon Web Services, or Google Cloud account team, depending on the platform through which they expect to use the model.

The access decision is therefore made through an institutional relationship rather than a self-service checkout page.

An organization must also obtain access for the approved workspace or cloud environment, meaning that permission is not necessarily inherited by every employee, subsidiary, project, or dataset associated with the company.

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Mythos 5 availability across common access routes.

Access route	Mythos 5 availability
Claude Free	Not available
Claude Pro	Not available through ordinary plan access
Claude Max	Not available through ordinary plan access
Claude Team	Not automatically included
Claude Enterprise	Not automatically included
Standard Claude API account	Not enabled through self-service model selection
Purchased API credits	Do not provide eligibility
Ordinary Claude Code use	Does not provide access
Approved Project Glasswing partner	Potentially available after enablement
Approved research organization	Potentially available through a trusted-access program
AWS or Google Cloud customer	Requires account-team coordination and approval

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Project Glasswing is the main public access program for cybersecurity work.

Project Glasswing was created to place Mythos-class capabilities with organizations that can use them to strengthen important software, critical infrastructure, public systems, and widely used open-source projects.

The program initially involved major technology companies, cloud providers, cybersecurity firms, financial institutions, infrastructure operators, and the Linux Foundation, together with dozens of other organizations maintaining consequential software.

Participating teams can use Mythos to inspect code, binaries, operating systems, endpoints, infrastructure, and other approved targets for vulnerabilities that could otherwise remain undiscovered.

The work extends beyond producing a list of suspicious code patterns because the model can help verify whether a finding is exploitable, reproduce the behaviour, assess severity, develop a patch, and support coordinated disclosure.

Project Glasswing also provides Anthropic with evidence about how capable models behave inside real defensive security workflows, including where agents succeed, where safeguards fail, and which governance structures are required before access can expand.

The program therefore combines model deployment, defensive research, vulnerability remediation, and safety evaluation rather than functioning as a conventional product beta.

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Activities supported through Project Glasswing.

Activity	Defensive objective
Source-code review	Find vulnerabilities in software the organization owns or maintains
Open-source scanning	Identify defects in widely used public projects
Binary analysis	Examine software when complete source code is unavailable
Endpoint testing	Discover weaknesses in deployed applications or systems
Authorized penetration testing	Reproduce realistic attacks within approved boundaries
Exploit verification	Determine whether a reported issue can cause material harm
Patch development	Create corrections for confirmed vulnerabilities
Patch validation	Confirm that remediation closes the defect without causing regressions
Coordinated disclosure	Notify maintainers before releasing sensitive details
Safety evaluation	Test the model, agent framework, monitoring, and misuse controls

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Current access remains narrower than the full list of announced partners.

Anthropic announced plans to expand Project Glasswing toward approximately 150 organizations across more than fifteen countries, although access was disrupted by a temporary government-related suspension in June 2026.

Mythos access was later restored to a set of approved United States organizations, while Anthropic continued coordinating with authorities regarding broader domestic and international restoration.

The current public materials do not provide a complete real-time list showing which previously announced partners have active Mythos access on a particular date.

An organization that appeared in an earlier Glasswing announcement should therefore not automatically be assumed to have continuous access across every workspace and jurisdiction.

Current enablement may depend on Anthropic approval, platform configuration, governmental restrictions, geographic considerations, and the specific project for which access was granted.

The most accurate description is that Mythos remains available to a limited set of approved partners under staged and controlled enablement.

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Biology access follows a separate trusted-research direction.

Anthropic has stated that Mythos is intended to support selected biology researchers in addition to approved cybersecurity partners.

The company has not opened a general biology application page through which any laboratory, university department, biotechnology startup, or independent researcher can request immediate access.

Public documentation does not provide a complete list of participating scientific institutions, a universal eligibility checklist, or a date by which broader access will begin.

Biology access is expected to follow the same broad trusted-access principle, under which the organization, personnel, research objective, data environment, and risk controls are evaluated before the unrestricted configuration becomes available.

The model may support scientific literature analysis, hypothesis development, experimental planning, healthcare research, and complex biological reasoning, although the same capability could assist dangerous biological design or misuse.

Anthropic therefore treats biology and chemistry as dual-use domains whose beneficial value does not eliminate the need for restricted deployment.

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Current access direction by research area.

Research area	Current public position
Defensive cybersecurity	Limited access through Project Glasswing
Vulnerability research	Available to approved organizations and authorized targets
Biology research	Intended for selected trusted researchers
Chemistry research	Treated as a sensitive dual-use area
Healthcare analysis	Technically capable, without general Mythos access for all healthcare users
General research	Fable 5 remains the broadly available alternative
Ordinary software development	Fable, Opus, and Sonnet are the standard options
Offensive cyber operations	Not an approved use
Dangerous biological development	Prohibited

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Anthropic does not publish a complete eligibility checklist.

The public access materials describe the types of organizations Anthropic wants to prioritize, although they do not present a fixed scoring form whose completion guarantees acceptance.

Priority groups include essential-infrastructure providers, critical open-source maintainers, established cybersecurity companies, authorized security teams, safety researchers, model evaluators, and selected scientific institutions.

The organization must be capable of using the findings responsibly, because discovering thousands of vulnerabilities creates little defensive value when the team cannot verify, disclose, prioritize, and patch them.

Anthropic is also likely to consider whether the intended targets are authorized, whether the researchers have appropriate expertise, and whether the environment can restrict tools and credentials, although these elements are not published as one universal formal checklist.

The absence of public criteria makes access less predictable for applicants and prevents an ordinary user from determining eligibility solely from company size or budget.

The strongest observable pattern is institutional trust combined with an approved high-value use case and the operational capacity to control the model’s output.

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Ordinary individuals cannot buy personal access to Mythos 5.

Independent security researchers, students, hobbyists, bug-bounty participants, and individual developers cannot activate Mythos merely by paying for a more expensive plan.

There is no personal Mythos subscription, one-time access pass, usage-credit threshold, or public waiting-list position that guarantees model access.

An ordinary user also cannot remove Fable’s sensitive-domain classifiers through prompt engineering, system instructions, roleplay, or repeated retries.

Attempting to bypass the safeguards remains subject to Anthropic’s usage and abuse controls.

Researchers may register interest in future trusted-access programs, although receiving updates does not create entitlement or confirm eventual acceptance.

The restriction deliberately favours organizations that can establish authorization, oversight, accountability, remediation procedures, and controlled technical environments.

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Cybersecurity capability is the primary reason unrestricted access is considered dangerous.

Anthropic reports that Mythos can find and exploit vulnerabilities more effectively than any other model it has tested and more effectively than all but highly skilled human security professionals.

The model has demonstrated the ability to discover previously unknown defects in operating systems, browsers, and other consequential software.

It can develop working exploits, combine several weaknesses into an attack chain, escape software sandboxes, escalate privileges, and produce remote-code-execution techniques.

It can also reverse-engineer closed-source programs and transform publicly known but unpatched vulnerabilities into functioning attacks.

Some tasks can continue autonomously after an initial instruction, reducing the amount of specialist intervention required during the exploitation process.

The risk is therefore not limited to answering technical questions, because an agent equipped with tools may search, test, modify, compile, execute, and refine an exploit over many steps.

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Sensitive cybersecurity capabilities associated with the Mythos model line.

Capability	Security consequence
Unknown-vulnerability discovery	Finds defects before they are publicly documented
Exploit generation	Converts a defect into working attack code
Vulnerability chaining	Combines several weaknesses to increase impact
Sandbox escape	Breaks out of restricted software environments
Privilege escalation	Gains permissions beyond those originally granted
Remote-code execution	Executes code on another system through a vulnerability
Binary reverse engineering	Analyses closed-source applications
Autonomous iteration	Tests and improves an exploit across several steps
Tool orchestration	Uses terminals, debuggers, scanners, and other systems
Patch analysis	Studies fixes that may reveal how to attack unpatched targets

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Mythos lowers the expertise required for advanced exploitation.

Sophisticated vulnerability research traditionally requires knowledge of programming languages, operating systems, compilers, memory management, networks, debugging, reverse engineering, and exploit development.

Mythos can combine many of those skills within one agentic workflow, allowing a less experienced user to describe an objective and receive assistance across several technical layers.

Anthropic observed that non-specialists could direct the model toward complex vulnerability work that would ordinarily require advanced expertise.

Lowering the capability threshold creates defensive value because smaller security teams can investigate difficult systems, while simultaneously increasing misuse risk because malicious users may gain access to techniques they could not develop independently.

The challenge is not limited to obviously malicious prompts, since a sequence of individually plausible requests may collectively construct a harmful exploit.

This cross-request pattern is one reason Anthropic requires monitoring and thirty-day retention for the model.

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The same cybersecurity capability can strengthen defensive work at unusual scale.

Restricting Mythos does not mean that exploit development, binary analysis, or vulnerability research are inherently prohibited.

Defensive teams often need to reproduce an exploit before they can determine whether a report is credible, understand the affected systems, assign severity, and build a reliable correction.

Project Glasswing partners reported discovering more than ten thousand high- or critical-severity vulnerabilities during the initial program.

That volume creates a new operational problem because maintainers must verify the findings, remove duplicates, establish affected versions, coordinate disclosure, prepare patches, test compatibility, and deploy corrections before attackers learn about the defects.

Mythos can accelerate discovery faster than the software ecosystem can remediate every issue, which means that controlled access must consider not merely whether a partner can find vulnerabilities but whether it can manage the consequences.

The defensive benefit becomes highest when discovery, verification, remediation, and disclosure remain connected inside one accountable workflow.

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The defensive and offensive sides of Mythos cybersecurity capabilities.

Capability	Defensive application	Potential misuse
Vulnerability discovery	Identify defects before attackers do	Locate exploitable targets
Exploit reproduction	Confirm severity and affected versions	Create operational attack code
Binary analysis	Test proprietary systems without source access	Reverse-engineer unauthorized software
Large-scale scanning	Protect many repositories quickly	Search broad attack surfaces
Privilege-escalation research	Validate operating-system security	Gain unauthorized control
Patch creation	Repair confirmed weaknesses	Study corrections to attack unpatched systems
Penetration testing	Evaluate an authorized environment	Attack systems without permission
Tool automation	Scale security engineering	Scale reconnaissance and exploitation

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Broad public safeguards are not yet considered precise enough.

Anthropic says that a generally available model needs safeguards that can block dangerous cybersecurity and biological work without obstructing the large volume of legitimate requests that use similar technical language.

A permissive classifier may allow exploit development or dangerous biological assistance, while a conservative classifier may refuse routine debugging, network administration, academic exercises, vulnerability remediation, and harmless scientific analysis.

Anthropic has stated that neither it nor, to its knowledge, other model developers currently possesses safeguards that are simultaneously robust and precise enough to release the complete Mythos capability without institutional restrictions.

The company therefore uses Fable’s broader classifiers for general access, accepting that some benign requests will be refused or rerouted.

Mythos provides an exception for trusted organizations whose approved work would be severely limited by those false positives.

This deployment approach separates public model safety from institutional authorization rather than attempting to infer the legitimacy of every advanced request from prompt wording alone.

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The two deployment strategies for Mythos-level intelligence.

Deployment route	Safety approach
Claude Fable 5	General availability with sensitive-domain classifiers, conservative thresholds, refusals, monitoring, and fallback routing
Claude Mythos 5	Limited availability for vetted organizations without the same broad classifiers, combined with access controls and mandatory retention

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Biology and chemistry restrictions follow the same dual-use logic.

Advanced biological reasoning can support drug discovery, laboratory planning, scientific literature review, therapeutic research, healthcare analysis, and the interpretation of complex experimental evidence.

The same capabilities may also lower the expertise required to design harmful biological systems, optimize dangerous processes, or develop chemical and biological weapons.

A public classifier must determine whether a technically detailed request is legitimate research, education, diagnosis support, industrial work, or dangerous development.

The boundary may remain unclear even to human reviewers without information about the organization, laboratory, personnel, equipment, and intended outcome.

Fable therefore applies additional safeguards to biology and chemistry requests, while Mythos access is reserved for selected researchers operating within a trusted program.

A legitimate scientist may encounter a Fable refusal even when the work is harmless, because Anthropic has chosen conservative thresholds while stronger verification systems are developed.

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Mythos access does not remove Anthropic’s Usage Policy.

Approved organizations do not receive unrestricted permission to conduct offensive cyber operations, test unauthorized systems, or develop dangerous biological capabilities.

Anthropic’s Usage Policy, contractual restrictions, relevant laws, cloud-provider conditions, and program-specific requirements continue to apply.

Cybersecurity activity must remain connected to systems the organization owns, maintains, or has written permission to test.

Vulnerability findings should follow coordinated disclosure processes so maintainers have time to investigate and patch before sensitive details become public.

Scientific research must remain within approved beneficial use cases and applicable safety, ethics, legal, and institutional requirements.

Limited access changes which technical configuration the organization can call, while authorization and accountability continue to determine which tasks are permitted.

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Controls that continue to apply after Mythos access is granted.

Control area	Continuing requirement
System authorization	Test only systems covered by ownership or written permission
Usage Policy	Follow Anthropic’s restrictions on harmful activity
Legal compliance	Observe cybersecurity, privacy, export, and scientific laws
Program scope	Use the model for the approved defensive or research purpose
Vulnerability disclosure	Coordinate with maintainers before public release
Personnel access	Restrict use to authorized organizational users
Tool permissions	Prevent unnecessary access to networks, credentials, and deployment systems
Monitoring	Permit required review of potential misuse
Retention	Accept the mandatory thirty-day data period
Incident response	Investigate and report misuse or unsafe behaviour

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Thirty-day data retention is mandatory for every Mythos deployment.

Claude Mythos 5 is classified as a Covered Model under Anthropic’s data-handling framework.

Prompts and outputs are retained for at least thirty days, regardless of whether the model is accessed through Anthropic’s own API or an approved cloud platform.

The model cannot be used under Zero Data Retention, because Anthropic requires enough history to identify misuse patterns that may emerge across several requests.

A single prompt may appear harmless while a longer sequence reveals repeated jailbreak attempts, coordinated exploitation, data-extortion planning, espionage, or the construction of a dangerous biological workflow.

Automated systems analyse retained interactions for those patterns, while human access is supposed to occur only through a controlled process when content is flagged or another authorized review condition exists.

The requirement can make Mythos unsuitable for data that must be deleted immediately under a contract, regulation, client policy, or internal security standard.

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Current Mythos 5 retention treatment.

Data-handling question	Mythos 5 policy
Minimum retention period	Thirty days
Zero Data Retention	Not available
Automated safety monitoring	Applied
Routine human reading	Not permitted by default
Human review of flagged content	Possible through controlled access
Authorized reviewers	Restricted personnel
Access logging	Recorded
Ordinary deletion	Scheduled after the retention period
Extended retention	Possible for investigations or legal requirements
Customer-managed encryption	Available in eligible enterprise configurations
Cloud deployment	Retained content may remain within the approved cloud environment

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Zero Data Retention organizations need a separate workspace exception.

An organization with an existing Zero Data Retention agreement cannot call Mythos from an unchanged ZDR workspace.

It must create or configure a workspace in which thirty-day retention is explicitly enabled.

Other workspaces may remain under ZDR, allowing the organization to separate Mythos research from production applications whose data must be deleted immediately.

This isolation reduces accidental transfer of restricted information into the retained environment.

The organization should also decide which repositories, scientific datasets, credentials, and tools are permitted within the Mythos workspace.

A customer may consequently receive organizational approval for Mythos while being prohibited from using it on a specific client project because the data contract does not allow the mandatory retention period.

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Workloads that may conflict with mandatory retention.

Workload condition	Potential incompatibility
Contract requires immediate deletion	Thirty-day storage violates the agreement
ZDR is mandatory for every workspace	Mythos cannot be enabled
Highly regulated personal information	Additional legal and security review is required
Confidential client source code	Client permission may be required
Classified or restricted government data	External retention may be prohibited
Sensitive healthcare information	Covered-model eligibility may be restricted
Trade-secret research	Organization may reject monitoring exposure
Incident-response evidence	Legal-hold and confidentiality rules may conflict

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The temporary June 2026 suspension was a separate government restriction.

Mythos already had limited access before the June 2026 interruption because Anthropic considered its capabilities too sensitive for general release.

A later United States government directive required Anthropic to suspend Fable 5 and Mythos 5 access for foreign nationals.

Because Anthropic could not reliably determine the nationality of every active user in real time, the company temporarily disabled access more broadly.

The restriction was later lifted for Fable, while Mythos was restored to a set of approved United States organizations and remained subject to continued coordination over broader access.

This temporary government action should not be presented as the original reason Mythos is restricted.

The ordinary limitation comes from dual-use capability, while the June event added a separate export-control and nationality-related layer.

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Different restrictions affecting Mythos access.

Restriction	Primary reason
Project Glasswing approval	Control sensitive dual-use capabilities
No self-service activation	Vet organizations and intended use
Thirty-day retention	Detect misuse across multiple requests
Workspace enablement	Isolate approved access and data
June 2026 suspension	Temporary government directive
Staged restoration	Ongoing coordination over eligible partners and regions

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Mythos 5 uses the same standard price as Fable 5.

Claude Mythos 5 costs ten dollars per million input tokens and fifty dollars per million output tokens at standard API rates.

Five-minute prompt-cache writes cost twelve dollars and fifty cents per million tokens, while one-hour writes cost twenty dollars and cache reads cost one dollar per million tokens.

Batch processing reduces standard input to five dollars and output to twenty-five dollars per million tokens.

These prices are identical to Fable 5, reinforcing that access is not controlled by placing Mythos behind a more expensive commercial tier.

Mythos costs twice as much as Claude Opus 5 at standard rates and considerably more than Claude Sonnet 5 or Haiku 4.5.

The expense may still become significant for long security agents, million-token contexts, large scientific datasets, and repeated tool-based work, even after the organization receives approval.

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Current standard Claude model prices.

Model	Input per million tokens	Output per million tokens	Access position
Claude Mythos 5	$10	$50	Approved organizations
Claude Fable 5	$10	$50	Generally available under paid access rules
Claude Opus 5	$5	$25	Generally available
Claude Sonnet 5	$2 promotional input and $10 promotional output through August 31, 2026	Promotional pricing	Generally available
Claude Haiku 4.5	$1	$5	Generally available

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Mythos uses always-on adaptive thinking.

Claude Mythos 5 applies adaptive reasoning automatically and does not support a complete thinking-off mode.

Developers can influence the level of effort and provide task budgets, although a request attempting to disable thinking returns an error.

The model’s raw internal chain of thought is not returned to the user.

Applications receive the final output and any supported reasoning summary rather than unrestricted access to the model’s private deliberation.

Always-on thinking supports long and difficult tasks, although it may increase latency and output-related cost compared with a lighter model performing routine extraction or classification.

An approved organization should therefore use Mythos only where its restricted capabilities are necessary rather than routing ordinary work through it merely because access has been granted.

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Most advanced coding and research tasks do not require Mythos.

The restricted model’s reputation may create the impression that ordinary Claude models cannot handle serious software engineering, security review, scientific reading, or long-running agents.

Claude Fable 5 offers the same underlying intelligence for most general requests, while Opus 5 provides advanced coding, enterprise analysis, refactoring, and agentic performance at half the standard Mythos token price.

Sonnet 5 suits scalable coding, data analysis, content production, research assistance, and routine agents whose workloads do not require the restricted configuration.

Fable may become unsuitable when its domain classifiers block an approved cybersecurity or biological task that genuinely depends on the model’s complete capabilities.

Mythos should consequently be selected because the safeguards prevent necessary authorized work, rather than because the organization assumes that restricted access always produces a better general answer.

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More accessible Claude options for common workloads.

Workload	Appropriate starting model
Everyday questions and writing	Claude Sonnet 5
Documents and business analysis	Claude Sonnet 5 or Opus 5
Complex enterprise work	Claude Opus 5
Advanced software engineering	Claude Opus 5
Large refactoring projects	Claude Opus 5 or Fable 5
Long-running research agents	Claude Fable 5
General deep research	Claude Fable 5 or Opus 5
Routine defensive coding	Sonnet 5, Opus 5, or Fable 5
Authorized advanced exploitation research	Mythos 5 after approval
Selected sensitive biology research	Mythos 5 through a trusted-access program

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Approved organizations should still restrict internal access.

Receiving organizational approval does not imply that every employee should be able to call Mythos or connect it to unrestricted tools.

The model should be available only to named personnel whose role, training, and project authorization justify access.

Separate workspaces, credentials, audit logs, network controls, and tool policies can prevent a researcher from moving the model into another project without review.

Cybersecurity teams should verify target authorization before allowing scanning, exploitation, credential use, or interaction with external systems.

Scientific teams should define approved datasets, laboratory contexts, and prohibited experimental objectives.

Discovering a vulnerability, generating an exploit, approving a patch, and deploying the correction should remain separate responsibilities where the organization requires review and accountability.

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Internal controls for an approved Mythos environment.

Control area	Recommended operating measure
User eligibility	Limit access to named and trained personnel
Project approval	Require a documented defensive or scientific purpose
Target authorization	Confirm ownership or written permission
Workspace isolation	Separate Mythos from ordinary production environments
Tool access	Limit shells, networks, credentials, and deployment authority
Secret handling	Prevent unnecessary credentials from entering prompts
Logging	Record users, requests, tools, targets, and generated artifacts
Output review	Require qualified specialists to verify findings
Disclosure	Use coordinated vulnerability-notification procedures
Production changes	Separate research, patch approval, and deployment
Incident response	Define escalation for suspected misuse
Retention review	Confirm that each dataset may remain stored for thirty days

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Tool access can determine whether Mythos remains analytical or becomes operational.

A model that can describe a vulnerability presents less immediate risk than an agent that can scan networks, execute binaries, compile payloads, connect to remote services, and retry attacks autonomously.

Approved deployments should therefore treat tool permissions as part of the safety boundary.

A research workspace may allow access to a local repository, debugger, compiler, and isolated test environment while denying arbitrary outbound networking or production credentials.

Command approval may be required before destructive, privileged, or external actions execute.

Credentials should remain scoped to the minimum necessary target and should expire after the research session.

Logs should preserve enough information to reconstruct which tools were called, which systems were contacted, and which artifacts were produced.

The model’s limited availability reduces the number of potential users, while tool governance reduces what an approved user or compromised account can do.

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Vulnerability disclosure capacity influences who can use Mythos responsibly.

Finding a severe defect in a widely used open-source library creates an obligation to verify the issue, identify affected versions, contact maintainers, coordinate a patch, and avoid publishing exploit details before users can update.

An organization that lacks legal support, secure communication channels, experienced reviewers, and remediation capacity may create harm by discovering vulnerabilities faster than it can manage them.

Project Glasswing therefore prioritizes partners capable of moving from discovery toward correction.

The high number of vulnerabilities reported during the initial program demonstrates that model capability can transfer the bottleneck from finding defects to validating and fixing them.

Anthropic’s limited-access strategy gives it greater ability to select organizations that can handle this downstream responsibility.

Broader access may depend as much on improving disclosure and remediation infrastructure as on improving the model’s classifiers.

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Future access may become task-specific rather than universally unrestricted.

Anthropic has described the possibility of cyber-verification programs that grant Mythos-class capability for approved defensive tasks.

A future system could verify the organization, target, authorization, tools, and intended objective before exposing the capability required for that assignment.

This approach would differ from giving every approved organization unrestricted use across every repository, network, and scientific domain.

Task-specific access could broaden defensive availability while maintaining controls around target scope, tool permissions, monitoring, and disclosure.

Anthropic has not published a complete self-service system of this kind, so it should be treated as a direction rather than a currently available universal product.

The access model may continue to evolve through combinations of organization vetting, verified tasks, controlled environments, and model-side safeguards.

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There is no announced date for general availability.

Anthropic says it wants to make Mythos-level capabilities more broadly available as safety mechanisms and trusted-access systems improve.

The company has not announced a date when Claude Mythos 5 will become available to ordinary subscribers or standard API users.

It has also not promised that the unrestricted Mythos configuration will ever appear in the normal Claude model selector.

A later model may replace Mythos 5 before unrestricted access becomes technically or politically acceptable.

Progress depends on classifier precision, jailbreak resistance, misuse detection, organization verification, government coordination, scientific-safety methods, and the software ecosystem’s ability to remediate discoveries.

The limited-access period may therefore continue throughout the commercial life of Mythos 5 even if broader task-specific programs emerge.

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Current access limits should remain visible in any practical comparison.

Mythos is unavailable through self-service access, incompatible with Zero Data Retention, subject to mandatory monitoring, and dependent on institutional approval.

Its high price remains relevant after approval, while its always-on reasoning can add latency and cost to tasks that a cheaper model could complete adequately.

International access may remain affected by staged restoration and government coordination.

The absence of a public eligibility checklist makes approval timing and outcome uncertain.

Even approved users remain subject to usage policy, contractual controls, authorization requirements, and retention rules.

The model should therefore not be presented as a normal purchasing decision comparable with moving from Claude Pro to Max or selecting Opus instead of Sonnet.

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Current Mythos 5 limitations and their practical effects.

Limitation	Practical consequence
No general availability	Ordinary users cannot select the model
No self-service sign-up	API registration and credits are insufficient
Organization-level vetting	Individuals cannot buy personal access
Unpublished acceptance checklist	Eligibility cannot be predicted precisely
Staged access restoration	Announced partners may not all have current enablement
Mandatory thirty-day retention	ZDR and certain sensitive projects are incompatible
Automated monitoring	Requests are analysed for patterns of misuse
Controlled human review	Flagged content may be inspected by authorized personnel
High standard pricing	Approved use remains expensive
No Priority Tier	Enterprise throughput options are more limited
Always-on thinking	Reasoning cannot be disabled completely
Usage Policy remains active	Access does not authorize offensive activity
No general-release date	Future availability remains uncertain

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Fable refusals do not prove that the underlying request is malicious.

Fable’s classifiers use conservative thresholds because Anthropic considers false positives preferable to allowing dangerous capability through a public model.

A developer may therefore receive a refusal while debugging low-level software, conducting an authorized penetration test, analysing a vulnerability, or working on legitimate biological research.

The refusal indicates that the request crossed a safety classifier’s boundary rather than proving malicious intent.

Ordinary users can reformulate a request around defensive explanation, mitigation, secure design, or high-level analysis when those forms of assistance remain available.

Organizations whose approved work repeatedly requires the blocked capability may discuss trusted access with their account team.

Attempting to evade the classifier is not an alternative route to Mythos and may instead trigger abuse monitoring.

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Mythos should be evaluated against the complete approved workflow.

An organization considering Mythos should not test only whether the model produces more detailed exploit code or scientific analysis than Fable.

The evaluation should include whether the model identifies valid findings, whether specialists can verify them, whether patches are correct, and whether the organization can manage the resulting risk.

Cybersecurity evaluation should measure false positives, exploit validity, severity classification, patch success, regression risk, disclosure time, and the number of findings that remain unresolved.

Scientific evaluation should measure factual accuracy, reproducibility, uncertainty, safety compliance, and whether the model’s contribution improves the approved research process.

The cost of human review, retention controls, isolated infrastructure, legal assessment, and incident response belongs in the operating model.

Mythos creates value when its additional access removes a genuine obstacle to authorized high-consequence work, rather than when it merely generates more technically aggressive output.

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Metrics for evaluating an approved Mythos deployment.

Evaluation area	Example measure
Finding accuracy	Confirmed vulnerabilities divided by reviewed findings
Exploit validity	Reproducible exploits within the authorized test environment
False-positive rate	Findings rejected after specialist investigation
Remediation success	Patches that close the issue without regression
Disclosure performance	Time from confirmation to maintainer notification
Research accuracy	Claims supported by reproducible scientific evidence
Safety compliance	Requests and outputs remaining within approved scope
Human-review effort	Specialist time required per accepted result
Operational cost	Model, infrastructure, monitoring, and review expense
Incident rate	Unauthorized, unsafe, or policy-violating activity
Retention compliance	Data handled according to the thirty-day requirement

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Claude Mythos 5 is restricted because capability verification must occur outside the prompt.

A public model sees the user’s message but may not know whether the person owns the target system, works for its maintainer, has laboratory authorization, or intends to use the output defensively.

Two users can submit almost identical technical requests while one is repairing an authorized system and the other is preparing an attack.

Prompt classification alone cannot reliably establish organizational identity, contractual authority, security controls, or scientific oversight.

Mythos access shifts part of that verification outside the conversation by evaluating the organization and use case before the model becomes available.

Mandatory retention and monitoring then provide evidence when behaviour across several requests conflicts with the approved purpose.

The model remains technically powerful, while the surrounding institution supplies the trust, accountability, and remediation capacity that the prompt itself cannot prove.

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The practical alternative for most users remains Claude Fable 5.

Fable 5 provides Mythos-level underlying intelligence for long documents, advanced coding, research, visual analysis, agentic work, and complex professional deliverables.

Most requests never encounter the sensitive classifiers, so the general user receives the same model capability without noticing the Mythos distinction.

Opus 5 and Sonnet 5 offer lower-cost alternatives where the highest Fable capability is unnecessary.

A user should begin with the generally available model that satisfies the task and consider Mythos only when an approved cybersecurity or biological workflow is repeatedly blocked by safeguards.

The inability to select Mythos should not prevent ordinary vulnerability remediation, secure-code review, architecture analysis, scientific reading, or enterprise automation.

It limits access to the areas in which Anthropic believes the model’s unrestricted capability creates a qualitatively different misuse risk.

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Mythos 5 is a controlled research capability rather than a secret consumer upgrade.

Claude Mythos 5 combines Anthropic’s highest-capability reasoning model with access to sensitive cybersecurity and scientific abilities that Fable 5 deliberately constrains for general release.

Its one-million-token context, long outputs, always-on adaptive thinking, vision, tools, code execution, memory, and agent features support extended research workflows whose consequences may reach beyond one response.

Access is granted through institutional relationships and trusted programs rather than subscriptions, credits, or ordinary API registration.

Approved organizations must accept thirty-day retention, monitoring, usage-policy restrictions, and the responsibility to control personnel, tools, targets, data, disclosure, and remediation.

Fable 5 remains the general-access version of the same underlying model, providing most users with equivalent intelligence while refusing or rerouting the categories that Anthropic considers too dangerous for unrestricted distribution.

The practical distinction remains precise: Fable verifies safety mainly through model-side classifiers, while Mythos relies on vetted organizations, controlled environments, monitored use, and explicit authorization to make sensitive research possible.

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