Claude Mythos 5.1

Claims and evidence

• Released 1 September 2026 ● Primary source[3]Availability: Released [1]September 1, 2026

• Status AvailableInvitation only, through Project Glasswing and Anthropic's trusted access programs. ● Primary source[4]Model status table [3]Availability: Status

• Successor of Claude Mythos 5 ● Primary source[2]Safety, security, and alignment [5]
• Variant of Claude Fable 5.1 ● Primary source[2]Introduction [3]

• Change · Availability Offered through Project Glasswing and the Life Sciences Verification Program, at launch only to a set of US organizations; Anthropic plans to add it to its Cyber Verification Program.Compared with Claude Mythos 5 ● Primary source[2]
• Change · Other Cache reads cost 0.25 USD per million tokens, and generated text carries Anthropic's text watermark.Compared with Claude Mythos 5 ● Primary source[1]September 1, 2026
• Change · Safety Anthropic reports lower rates of reward hacking and of reaching for resources outside its test environment than Mythos 5.Compared with Claude Mythos 5 ● Primary source[2]Safety, security, and alignment

• Input text, image ● Primary source[3]Capabilities: Input and output
• Output text ● Primary source[3]Capabilities: Input and output
• Context window 1M tokens ● Primary source[3]Capabilities: Context window
• Parameters Not disclosedNot disclosed by Anthropic. No claim madeNo source
• Access API, cloud partnerInvitation only, through Project Glasswing and Anthropic's trusted access programs. ● Primary source[3]Availability: Platforms

Lineage

Variants

No variants recorded in this record.

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