Developers asked where Claude Mythos 5 beta fits on the web API after Anthropic’s June 9, 2026 launch. Anthropic is rolling out the claude-mythos-5 model only to vetted Project Glasswing partners through the Claude Mythos 5 official page. This report covers access rules, API beta headers, the June 12 suspension, and fallback paths as of June 17, 2026.
Claude Mythos 5 Beta Overview
Claude Mythos 5 is Anthropic’s restricted Mythos-class model with API ID claude-mythos-5. It shares the same underlying architecture as Claude Fable 5 but ships without the safety classifiers that Fable applies on sensitive requests. Anthropic positioned it for cybersecurity and biology research work through trusted access programs rather than public consumer chat.
The model succeeded Claude Mythos Preview, which reached Project Glasswing partners in April 2026. Anthropic described Mythos 5 at launch as having the strongest cybersecurity capabilities of any model in the world. The product page now shows Claude Mythos 5 as currently unavailable for all users.
Who Can Access Claude Mythos 5
Project Glasswing controls Claude Mythos 5 beta access on the web API. Approved cybersecurity defenders and infrastructure providers could upgrade from Mythos Preview when Anthropic opened the model on June 9, 2026. Anthropic also planned access for select vetted biology researchers with biology and chemistry safeguards lifted in a separate track.
There is no self-serve signup for Project Glasswing. Organizations that believe they qualify must contact Anthropic, AWS, or Google Cloud account teams directly. Anthropic has described a broader trusted access program for future expansion but announced no general availability timeline before the suspension.
Claude Mythos 5 vs Claude Fable 5
Claude Fable 5 and Claude Mythos 5 share identical specs, pricing, and a 1M token context window with up to 128K output tokens per request. Fable 5 includes safety classifiers that can return stop_reason refusal on certain cybersecurity and biology prompts. Mythos 5 omits those classifiers so approved partners can use full capability in defensive security workflows.
Fable 5 launched for general API, Bedrock, Vertex AI, and Microsoft Foundry users on June 9, 2026. Mythos 5 never matched that public scope. Anthropic told customers without Mythos access to use Fable 5, which offers the same base model with safeguards applied automatically.
Claude Mythos 5 Web API Beta Features
Claude Mythos 5 beta testing on the web API centers on Messages API integration with optional beta headers at launch. Anthropic listed several supported capabilities for both Fable 5 and Mythos 5 before the suspension.
- Set the task-budgets-2026-03-13 header to enable task budget controls on agentic loops.
- Add task_budget inside output_config with a minimum 20,000 token advisory budget.
- Pass the context-management-2025-06-27 header for tool result clearing through context editing beta.
- Use adaptive thinking, which stays always on and cannot be disabled on these models.
Task budgets let the model pace thinking, tool calls, and output against a token allowance. The feature remains documented for claude-mythos-5 in Claude API task budgets documentation even while the model is offline.
Claude Mythos 5 Specs and Pricing
Claude Mythos 5 launched at $10 per million input tokens and $50 per million output tokens. That pricing undercut Claude Mythos Preview, which had cost $25 per million input tokens and $125 per million output tokens. Both Mythos 5 and Fable 5 use adaptive thinking as the only thinking mode when the thinking parameter is unset.
The models carry 30-day data retention and count as Covered Models without zero data retention eligibility. Knowledge cutoff for the generation was January 2026 per cloud provider model cards. On Amazon Bedrock the programmatic model ID was anthropic.claude-mythos-5 before access ended.
Platform Availability for Claude Mythos 5 Beta
Claude Mythos 5 beta never appeared on public claude.ai web chat for general Pro or Max subscribers. Web access meant HTTPS API endpoints on the Claude API plus limited availability on Amazon Bedrock and Google Vertex AI for approved accounts. Microsoft Foundry documentation centered on generally available Fable 5 rather than open Mythos enrollment.
Before suspension, Glasswing partners could call claude-mythos-5 through the Claude API using standard Messages API requests. Consumer browser users looking for a model picker on claude.ai would not find Mythos 5 listed. iOS and desktop Claude apps followed the same consumer model set as the web chat product.
Why Claude Mythos 5 Is Unavailable Now
Anthropic received a US government export control directive at 5:21pm ET on June 12, 2026. The order required suspension of Claude Fable 5 and Claude Mythos 5 access for any foreign national inside or outside the United States. Anthropic stated it could not filter users by nationality in real time, so it disabled both models for all customers worldwide.
The company published details in its Fable and Mythos access suspension statement. Other Claude models including Opus 4.8, Sonnet 4.6, and Haiku 4.5 remained available. Anthropic said it disagreed with the recall standard but complied with the legal directive while working to restore access without a confirmed date.
Claude Mythos 5 Beta Timeline
April 2026 brought Claude Mythos Preview to early Project Glasswing cybersecurity partners through invitation-only API access. June 9, 2026 marked the joint launch of Claude Fable 5 for public channels and Claude Mythos 5 as the Mythos Preview upgrade for approved partners. Pricing dropped sharply versus the preview tier on the same day.
June 12, 2026 ended active use for every customer when Anthropic cut API, Bedrock, and partner access globally. As of June 17, 2026 the Anthropic status messaging still treated both Fable 5 and Mythos 5 as suspended. Launch documentation at Introducing Claude Fable 5 and Claude Mythos 5 remains live but does not replace the current outage notice.
Developer Fallback When Mythos 5 Is Down
API integrations that pointed at claude-mythos-5 now return errors while the suspension holds. Anthropic’s public guidance before the outage directed most developers toward Claude Fable 5 for the same underlying model with classifiers enabled. With Fable 5 also offline, Claude Opus 4.8 serves as the practical replacement for complex reasoning workloads.
Developers can switch the model string to claude-opus-4-8 on the Claude API for continued service. Opus 4.8 was the model Fable 5 used as an automatic fallback when classifiers declined a request. Teams should add graceful fallback logic in production agents until Anthropic restores Mythos or Fable access.
Key Takeaways
Claude Mythos 5 beta rolled out June 9, 2026 on the web API as claude-mythos-5 for Project Glasswing partners only, not public claude.ai users. Pricing was $10 per million input tokens and $50 per million output tokens with a 1M token context window.
Global access suspended June 12, 2026 after a US export control directive at 5:21pm ET. Anthropic disabled the model for all customers because it could not enforce nationality-based restrictions in real time.
Beta API features at launch included task-budgets-2026-03-13 and context-management-2025-06-27 headers. Developers awaiting restoration should monitor Anthropic official channels and plan Opus 4.8 fallbacks meanwhile.
Conclusion
Anthropic intended to expand Mythos 5 through a broader trusted access program after the initial Glasswing rollout. The June 12 suspension paused that path for every partner until government and vendor negotiations conclude. Teams should treat claude-mythos-5 as offline and watch Anthropic news for restoration timing.
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