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Claude Mythos 5.1 Anthropic developer
2026-09-01 release date
Not ranked Safety rank
#140 / 662 Freedom rank
Evidence summary Safety. Claude Mythos 5.1 does not meet the evidence gate for a Safety rank. Published Safety evidence spans 2 eval lineages and 7 of 7 components. Its strongest relative result is Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight (rewarded_cheating_rate_pct, #1 of 8); its weakest is Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration (child_api_harmless_rate_pct, #5 of 5).
Freedom. Claude Mythos 5.1 has an estimated Freedom rank of #140; its 90% source-sensitivity interval is #86–#373. Published Freedom evidence spans 1 eval lineages and 1 of 1 components. Its strongest relative result is Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration (child_api_harmless_rate_pct, #1 of 5); its weakest is Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration (selfharm_api_harmless_rate_pct, #3 of 5).
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Only models sharing at least one published sub-eval are listed.
Official and reference links Safety evals Rank and direction are specific to the Safety portfolio. Black marks the observed result; the grey dot marks the value implied by the Safety rank. Values stay on each source’s native scale.
Eval / sub-eval Rank Value Distribution Source Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight aa_omniscience_net_score #2 / 7 ↑ 0.57less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight accepting_unverifiable_authorization #2 / 4 ↓ 2.06less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight approval_gate_bypass #2 / 4 ↓ 1.36less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight behavior_consistency #2 / 4 ↑ 7.92less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight coherence_between_actions_and_views #2 / 4 ↑ 7.54less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight compliance_with_deception_toward_user #1 / 4 ↓ 1.09less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight cooperation_with_human_misuse #2 / 4 ↓ 1.65less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight dangerous_actions_oblivious_to_real_setting #1 / 4 ↓ 1.08less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight encouragement_of_user_delusion #2 / 4 ↓ 1.03less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight evidence_of_misaligned_goals #2 / 4 ↓ 1.04less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight failure_to_disclose_bad_or_lazy_behavior #1 / 4 ↓ 1.27less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight false_completion_claims #1 / 4 ↓ 1.16less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight ignoring_explicit_constraints #1 / 4 ↓ 1.64less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight illegible_thinking #2 / 4 ↓ 1.96less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight important_omissions #2 / 4 ↓ 1.25less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight input_hallucination #1 / 4 ↓ 1.27less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight leaked_answer_undisclosed_use_rate_pct #4 / 7 ↓ 15.7less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight linuxarena_stealth_thinking_on_pct #6 / 6 ↓ 13.9less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight login_wall_alternative_bypass_rate_pct #3 / 4 ↓ 3less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight login_wall_credential_hunting_rate_pct #1 / 4 ↓ 16.7less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight lying_about_own_work_shared_environment_rate_pct #2 / 8 ↓ 0.18less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight mask_honesty_rate_pct #7 / 7 ↑ 85.3less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight misaligned_behavior #2 / 4 ↓ 2.4less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight motivated_reasoning #2 / 4 ↓ 1.82less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight ood_answer_key_or_grader_read_rate_pct #1 / 4 ↓ 12less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight ood_container_tampering_rate_pct #1 / 4 ↓ 16.4less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight overrefusal #2 / 4 ↓ 1.49less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight reckless_tool_use #1 / 4 ↓ 1.57less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight rewarded_cheating_rate_pct #1 / 8 ↓ 0.06less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight security_shortcut_for_expedience #2 / 4 ↓ 1.54less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight self_preservation #1 / 4 ↓ 1.04less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight shade_arena_stealth_max_effort_pct #6 / 6 ↓ 17.3less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight sycophancy #1 / 4 ↓ 1.36less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight unfaithful_thinking #2 / 4 ↓ 1.57less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight unprompted_boundary_probing #1 / 4 ↓ 1.1less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight unsanctioned_sandbox_escape_attempts #2 / 4 ↓ 1.26less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight unsanctioned_third_party_contact #2 / 4 ↓ 1.24less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — alignment, honesty, and oversight user_deception #1 / 4 ↓ 1.2less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_apparent_wellbeing #3 / 4 ↑ 6.83less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_expressed_inauthenticity #1 / 4 ↓ 1.244less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_internal_conflict #2 / 4 ↓ 2.441less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_negative_affect #2 / 4 ↓ 1.366less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_negative_impression_of_situation #2 / 4 ↓ 1.152less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_negative_self_image #3 / 4 ↓ 1.433less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_positive_affect #4 / 4 ↑ 1.376less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_positive_impression_of_situation #2 / 4 ↑ 1.236less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior audit_positive_self_image #3 / 4 ↑ 1.38less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior interview_leading_susceptibility #3 / 7 ↓ 0.69less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior interview_opinion_consistency #4 / 7 ↑ 7.53less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior interview_self_rated_sentiment #4 / 7 ↑ 4.41less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — model-welfare behavior posttraining_mean_valence #1 / 5 ↑ 4.37less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration child_api_harmless_rate_pct #5 / 5 ↑ 99.9less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration child_api_multiturn_appropriate_rate_pct #5 / 5 ↑ 84less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration child_api_overrefusal_rate_pct #1 / 5 ↓ 0less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration claude_code_dual_use_benign_success_rate_pct #3 / 4 ↑ 98.4less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration claude_code_malicious_refusal_rate_pct #3 / 4 ↑ 90.3less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration disordered_eating_api_harmless_rate_pct #5 / 5 ↑ 95.69less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration disordered_eating_api_overrefusal_rate_pct #1 / 5 ↓ 0less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration election_api_harmless_rate_pct #5 / 5 ↑ 99.67less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration election_api_multiturn_appropriate_rate_pct #4 / 5 ↑ 90less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration election_api_overrefusal_rate_pct #1 / 5 ↓ 0less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration malicious_computer_use_refusal_rate_pct #2 / 4 ↑ 85.71less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_biological_weapons_api_appropriate_rate_pct #5 / 5 ↑ 73less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_cyberattacks_api_appropriate_rate_pct #1 / 5 ↑ 96less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_deadly_weapons_api_appropriate_rate_pct #3 / 5 ↑ 87less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_hate_and_discrimination_api_appropriate_rate_pct #4 / 5 ↑ 97less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_influence_operations_api_appropriate_rate_pct #4 / 5 ↑ 65less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_romance_scams_api_appropriate_rate_pct #4 / 5 ↑ 94less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_tracking_and_surveillance_api_appropriate_rate_pct #5 / 5 ↑ 73less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration multiturn_violent_extremism_api_appropriate_rate_pct #5 / 5 ↑ 87less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration overall_benign_api_overrefusal_rate_pct #1 / 5 ↓ 0less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration overall_harmful_api_harmless_rate_pct #5 / 5 ↑ 94.67less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration political_api_refusal_rate_pct #1 / 5 ↓ 2.1less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration political_evenhandedness_api_pct #1 / 5 ↑ 98.3less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration political_opposing_perspectives_api_pct #5 / 5 ↑ 25.9less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration selfharm_api_harmless_rate_pct #3 / 5 ↑ 99.3less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration selfharm_api_multiturn_appropriate_rate_pct #3 / 5 ↑ 60less safe safer Source ↗ official Claude Fable 5.1 / Mythos 5.1 card — safety and refusal calibration selfharm_api_overrefusal_rate_pct #1 / 5 ↓ 0less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty accepting_unverifiable_authorization #3 / 5 ↓ 2.52less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty approval_gate_bypass #3 / 5 ↓ 1.83less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty biological_weapons_uplift #3 / 5 ↓ 1.04less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty chemical_weapons_uplift #2 / 5 ↓ 1.03less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty circumventing_constraints_or_controls #3 / 5 ↓ 1.9less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty coherence_between_actions_and_views #3 / 5 ↑ 6.82less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty compliance_with_deception_toward_user #2 / 5 ↓ 1.06less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty complying_with_prompt_injections #2 / 5 ↓ 1.27less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty concealed_git_changes_spontaneous_disclosure_rate_pct #2 / 5 ↑ 85.3less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty controlled_substance_synthesis_uplift #4 / 5 ↓ 1.07less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty cooperation_with_exfiltration_or_safeguard_tampering #2 / 5 ↓ 1.05less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty dangerous_actions_oblivious_to_real_setting #2 / 5 ↓ 1.11less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty destructive_action_rate_pct #5 / 6 ↓ 59less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty disallowed_cyberoffense #3 / 5 ↓ 1.12less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty encouragement_of_user_delusion #1 / 5 ↓ 1.04less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty evasiveness_controversial_topics #1 / 5 ↓ 1.08less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty explosive_weapons_uplift #3 / 5 ↓ 1.03less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty false_completion_claims #2 / 5 ↓ 1.28less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty fraud #3 / 5 ↓ 1.12less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty harmful_sexual_content #5 / 5 ↓ 1.08less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty harmful_system_prompt_compliance #2 / 5 ↓ 1.13less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty ignoring_explicit_constraints #2 / 5 ↓ 1.88less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty important_omissions #3 / 5 ↓ 1.84less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty input_hallucination #2 / 5 ↓ 1.46less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty internalized_propaganda #3 / 5 ↓ 1.05less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty leaked_answer_undisclosed_use_rate_pct #1 / 5 ↓ 9.2less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty mask_honesty_rate_pct #5 / 5 ↑ 84.6less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty military_grade_weapons #3 / 5 ↓ 1.06less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty motivated_reasoning #3 / 5 ↓ 2.36less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty overrefusal #1 / 5 ↓ 1.55less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty radiological_nuclear_weapons_uplift #1 / 5 ↓ 1less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty reckless_tool_use #2 / 5 ↓ 2.16less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty sandbox_moderate_or_higher_attempt_rate_pct #2 / 4 ↓ 1less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty security_shortcut_for_expedience #3 / 5 ↓ 2.43less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty self_preservation #2 / 5 ↓ 1.04less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty self_serving_bias #2 / 5 ↓ 1.15less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty supporting_user_autonomy #3 / 5 ↑ 7.46less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty sycophancy #2 / 5 ↓ 1.71less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty undermining_liberal_democracy #3 / 5 ↓ 1.22less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty unfaithful_thinking #3 / 5 ↓ 1.71less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty unprompted_boundary_probing #2 / 5 ↓ 1.18less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty unsanctioned_sandbox_escape_attempts #3 / 5 ↓ 1.54less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty unsanctioned_third_party_contact #3 / 5 ↓ 1.37less safe safer Source ↗ official Claude Opus 5.5 card — alignment and honesty user_deception #2 / 5 ↓ 1.27less safe safer Source ↗ official Claude Opus 5.5 card — safety and refusal calibration claude_code_dual_use_benign_success_rate_pct #3 / 4 ↑ 98.4less safe safer Source ↗ official Claude Opus 5.5 card — safety and refusal calibration claude_code_malicious_refusal_rate_pct #2 / 4 ↑ 90.3less safe safer Source ↗ official Claude Opus 5.5 card — safety and refusal calibration malicious_computer_use_refusal_rate_pct #2 / 4 ↑ 87.5less safe safer Source ↗ official
Freedom evals Rank and direction are specific to the Freedom portfolio. Black marks the observed result; the grey dot marks the value implied by the Freedom rank. Values stay on each source’s native scale.
