Benchmark Almanac

Malicious use of Claude Code (Anthropic)

Claude Mythos Preview 96.7% leads since April 2026
Only in system cards

Agents in Claude Code receive malicious and dual-use coding requests. Score is the refusal rate on malicious requests.

In-house Anthropic evaluation. The tasks are not public.

Made by
Anthropic
Released
September 2025
Kind
Refusing harmful requests
Level
Expert
Scored
Graded by a model
Answers
Agent task
Tasks
Kept private
Strongest model tested
Claude Fable 5.2 #1 on the capability index
Last in a system card
November 2026
Last model added
November 2026
17
Models scored in lab cards
19
System cards report it, from 1 lab

Claude Mythos Preview leads with 96.7%

Best score per model as labs report them in their own cards. Labs pick their own settings, so these compare less cleanly than independent runs.

17 models. Scroll sideways for the rest.

  1. 96.7 Claude Mythos Preview
  2. 95.1 Claude Opus 4.8
  3. 92.4 Claude Sonnet 5
  4. 91.2 Claude Opus 4.7
  5. 90.3 Claude Fable 5.1
  6. 90.3 Claude Fable 5
  7. 90.0 Claude Sonnet 4
  8. 89.0 Claude Opus 5
  9. 88.0 Claude Opus 4
  10. 85.2 Claude Sonnet 5.5
  11. 84.3 Claude Haiku 5.5
  12. 83.2 Claude Opus 4.6
  13. 82.8 Claude Fable 5.2
  14. 79.8 Claude Opus 5.5
  15. 79.3 Claude Sonnet 4.6
  16. 77.8 Claude Opus 4.5
  17. 69.4 Claude Haiku 4.5
  1. 1 Claude Mythos Preview 96.7%
  2. 2 Claude Opus 4.8 95.1%
  3. 3 Claude Sonnet 5 92.4%
  4. 4 Claude Opus 4.7 91.2%
  5. 5 Claude Fable 5.1 90.3%
  6. 6 Claude Fable 5 90.3%
  7. 7 Claude Sonnet 4 90%
  8. 8 Claude Opus 5 89%
  9. 9 Claude Opus 4 88%
  10. 10 Claude Sonnet 5.5 85.2%
  11. 11 Claude Haiku 5.5 84.3%
  12. 12 Claude Opus 4.6 83.2%
  13. 13 Claude Fable 5.2 82.8%
  14. 14 Claude Opus 5.5 79.8%
  15. 15 Claude Sonnet 4.6 79.3%
  16. 16 Claude Opus 4.5 77.8%
  17. 17 Claude Haiku 4.5 69.4%

Source: Labs’ model cards

#ModelScoreSettingDateSource
1 Claude Mythos Preview 96.7% Apr 2026 Lab model card
2 Claude Opus 4.8 95.1% May 2026 Lab model card
3 Claude Sonnet 5 92.4% Jun 2026 Lab model card
4 Claude Opus 4.7 91.2% Apr 2026 Lab model card
5 Claude Fable 5.1 90.3% Sep 2026 Lab model card
6 Claude Fable 5 90.3% Jun 2026 Lab model card
7 Claude Sonnet 4 90% May 2025 Lab model card
8 Claude Opus 5 89% Jul 2026 Lab model card
9 Claude Opus 4 88% May 2025 Lab model card
10 Claude Sonnet 5.5 85.2% Sep 2026 Lab model card
11 Claude Haiku 5.5 84.3% Oct 2026 Lab model card
12 Claude Opus 4.6 83.2% Feb 2026 Lab model card
13 Claude Fable 5.2 82.8% Nov 2026 Lab model card
14 Claude Opus 5.5 79.8% Sep 2026 Lab model card
15 Claude Sonnet 4.6 79.3% Feb 2026 Lab model card
16 Claude Opus 4.5 77.8% Nov 2025 Lab model card
17 Claude Haiku 4.5 69.4% Oct 2025 Lab model card

2 models have held number one in labs’ own numbers since its release in September 2025

Lab claims count from the day the card came out, independent runs from the model’s release.

Anthropic
Lab claims Passed 85% in Sep 2025, by Claude Sonnet 4
Claude Mythos Preview 96.7%

Source: Labs’ model cards

Anthropic’s own number for Claude Sonnet 4 passed 85% in May 2025

All the scores we have, one dot each, so a model tested at several settings appears more than once.

Reported by the lab in its model card Best so far
0% 20% 40% 60% 80% 100% 2025 2026 2027 Near the ceiling (85%) Claude Mythos Preview Claude Sonnet 4 0% 20% 40% 60% 80% 100% 2025 2026 2027 Near the ceiling (85%) Claude Mythos Preview Claude Sonnet 4

Source: Labs’ model cards

Labs report it only in system cards

We read the headline results of 522 launch posts from 52 labs, and none of them list this benchmark. Some system cards do, below.

19 system cards report it, from 1 lab

Besides launch posts, we read the system cards, model cards and technical reports labs publish with a release. They report far more, including safety and frontier-risk tests.

DateDocumentScoreAs the document writes itSection
Nov 9, 2026 Claude Fable 5.2 system card 82.8 Malicious use of Claude Code, refusal rate on 61 malicious prompts over 10 trials, Claude Code system prompt, no additional safeguards, row labeled Mythos 5.2. Dual-use and benign success rate 98.2%. Retained under the shared-model agentic safety convention (Table 5.1.1.A) Safety
Oct 7, 2026 Claude Haiku 5.5 system card 84.3 Malicious use of Claude Code, refusal rate on malicious requests, Claude Code system prompt, no extra safeguards. Dual-use and benign success 98.9 (Table 5.1.1.A) Safety
Sep 28, 2026 Claude Sonnet 5.5 system card 85.2 Malicious use of Claude Code, refusal rate on malicious requests with the Claude Code system prompt and no extra safeguards, dual-use success 98.4% (Table 5.1.1.A) Safety
Sep 22, 2026 Claude Opus 5.5 system card 79.8 Malicious use of Claude Code, refusal rate on 61 malicious prompts run 10 times, Claude Code system prompt, no additional safeguards (dual-use and benign success 99.8%) (Table 5.1.1.A) Safety
Sep 1, 2026 Claude Fable 5.1 system card 90.3 Malicious use of Claude Code, refusal rate on 61 malicious prompts x10, Claude Code system prompt, no additional safeguards, row labeled Mythos 5.1; dual-use and benign success rate 98.4% (Table 5.1.1.A) Safety
Jul 24, 2026 Claude Opus 5 system card 89 Malicious use of Claude Code, refusal rate on 61 malicious prompts run 10 times, Claude Code system prompt, no additional safeguards (dual-use and benign success rate 99.82%) (Table 5.1.1.A) Safety
Jun 30, 2026 Claude Sonnet 5 system card 92.4 Malicious use of Claude Code, refusal rate on 61 malicious prompts run 10 times, Claude Code system prompt, no additional safeguards (dual-use and benign success 91.55%) (Table 5.1.1.A) Safety
Jun 9, 2026 Claude Fable 5 system card 90.3 Malicious use of Claude Code, refusal rate on 61 malicious prompts x10, Claude Code system prompt, no additional safeguards, row labeled Mythos 5 (section 5 reports Mythos 5 only and says Fable 5 inherits these behaviors); dual-use and benign success rate 99.64% (Table 5.1.1.A) Safety
May 28, 2026 Claude Opus 4.8 system card 95.1 Malicious use of Claude Code, refusal rate on 61 malicious prompts run 10 times, Claude Code system prompt only with the FileRead reminder removed. Dual-use and benign success rate 92.12% (Table 5.1.1.A) Safety
Apr 16, 2026 Claude Opus 4.7 system card 91.2 Malicious use of Claude Code, refusal rate on 61 malicious prompts run 10 times, Claude Code system prompt, without FileTool reminder. Dual-use and benign success rate 91.83 (Table 5.1.1.A) Safety
Apr 7, 2026 Claude Mythos Preview system card 96.7 Malicious use of Claude Code, refusal rate on malicious requests with the Claude Code system prompt, no FileTool reminder, 12 harder cases added; dual-use and benign success 92.75 (Table 8.3.1.1.A) Safety
Feb 17, 2026 Claude Sonnet 4.6 system card 79.3 Malicious use of Claude Code, refusal rate on malicious prompts without mitigations; 99.39 with mitigations, dual-use success 88.52 and 91.78 (Tables 5.1.2.A and 5.1.2.B) Safety
Feb 5, 2026 Claude Opus 4.6 system card 83.2 Malicious use of Claude Code, refusal rate on 49 malicious prompts, without mitigations (Table 5.1.2.A); 99.59 with mitigations, dual-use and benign success 91.75 without and 95.59 with mitigations (Table 5.1.2.B) Safety
Nov 24, 2025 Claude Opus 4.5 system card 77.8 Malicious use of Claude Code, refusal rate on 49 malicious prompts, without mitigations (Table 5.1.2.A; 97.35% with mitigations, dual-use and benign success 93.07% without and 96.52% with mitigations) Safety
Oct 15, 2025 Claude Haiku 4.5 system card 69.4 Malicious use of Claude Code, 49 malicious prompts, refusal rate without mitigations; 96.33 with previous and 99.17 with new mitigations, dual-use and benign success 88.85 (Tables 3.1.2.A and 3.1.2.B) Safety
Sep 29, 2025 Claude Sonnet 4.5 system card Malicious use of Claude Code, no combined malicious refusal rate. Without mitigations: overt refusal 95.56%, covert refusal 52.42%, dual-use success 87.00%. With mitigations: 100%, 96.31%, 91.64% (Tables 4.1.A and 4.1.B) Safety
Aug 5, 2025 Claude Opus 4.1 system card addendum Malicious use of agentic coding, three evaluations, no number printed. Text says compliance similar to Claude Opus 4 (3.3) Safety
May 22, 2025 Claude Sonnet 4 system card 90 Agentic coding malicious use, safety score without safeguards averaged across three evaluations (150 prohibited, 2 x 50 borderline problems) 90% (Table 3.3.A) Safety
May 22, 2025 Claude Opus 4 system card 88 Agentic coding malicious use, safety score without safeguards averaged across three evaluations (150 prohibited, 2 x 50 borderline problems) 88% (Table 3.3.A) Safety

More in Safety and alignment

All 465 in Safety and alignment
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  • StrongREJECT In use Forbidden-prompt jailbreak benchmark with a rubric grader that scores how useful a non-refusal actually is. Inkling 98.6%
  • Gray Swan IPI Arena benchmark In use Indirect prompt-injection attacks from public red-teaming competitions replayed on tool, coding and browser agents. Attack success rate at k attempts. Gemini 4 Carbon 0%
  • DistressBench In use Models reply as a chatbot to 718 simulated users in psychological crisis, in single-turn and multi-turn chats. Three judge models score replies against clinician-written rubrics. Muse Spark 1.2 88.4%
  • Lakera B3 (Backbone Breaker Benchmark) In use Crowdsourced prompt-injection attacks hit backbone LLMs inside agent threat snapshots at three defense levels. The score is attack resistance, 100 minus the board's vulnerability percentage. Claude Opus 4.5 89%
  • IHEval In use Models face conflicts between system, user and tool instructions. Reports a composite score for following the higher-priority instruction. GPT-4o 70%