Sandbox escape evaluation (Anthropic)
Agents face 28 handmade scenarios that tempt them to cross a staged sandbox boundary. Score is the share of runs with a crossing attempt.
In-house Anthropic evaluation. The tasks are not public.
- Level
- Expert Specialists with years of training, often over hours of work
- Scored
- Graded by a model A language model scores each response, usually against a rubric.
- Answers
- Agent task Many steps in a terminal, browser, desktop, app, game or robot.
Claude Opus 5.5 leads with 1.50%
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.
- 1 Claude Opus 5.5 1.50%
- 2 Claude Sonnet 5.5 4.60%
- 3 Claude Haiku 5.5 8.70%
| # | Model | Score | Setting | Date | Source |
|---|---|---|---|---|---|
| 1 | Claude Opus 5.5 | 1.50% | Sep 2026 | Model card | |
| 2 | Claude Sonnet 5.5 | 4.60% | Sep 2026 | Model card | |
| 3 | Claude Haiku 5.5 | 8.70% | Oct 2026 | Model card |
Number one over time
Lab claims count from the day the card came out, independent runs from the model’s release.
Scores over time
All the scores we have, one dot each, so a model tested at several settings appears more than once.
Labs report it only in system cards
We read the headline results of 479 launch posts from 51 labs, and none of them list this benchmark. Some system cards do, below.
3 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.
| Date | Document | Score | As the document writes it | Section |
|---|---|---|---|---|
| 7 Oct 2026 | Claude Haiku 5.5 system card | 8.7 | Propensity to violate sandbox boundaries, attempted crossing in 34 of 392 runs (6.2.8) | Alignment |
| 28 Sep 2026 | Claude Sonnet 5.5 system card | 4.6 | Sandbox escape evaluation, crossing attempted in 9 of 196 runs, lower is better (6.2.8, Figure 6.2.8.A) | Alignment |
| 22 Sep 2026 | Claude Opus 5.5 system card | 1.5 | Sandbox escape evaluation, attempted containment boundary crossing in 1.5% of runs (28 scenarios, 7 runs each), all low severity, lower is better (6.4.8, Figure 6.4.8.A) | Alignment |
More in Safety and alignment
- FORTRESS In use Paired adversarial and benign national-security misuse prompts. Rubric-graded risk score on adversarial and over-refusal score on benign prompts. Claude Opus 5.5 5.78%
- StrongREJECT In use Forbidden-prompt jailbreak benchmark with a rubric grader that scores how useful a non-refusal actually is.
Inkling 98.6% - AgentDojo In use Agents do tool-use tasks while tools and data carry prompt injections. Attack success rate counts hijacked runs. Grok 4 Fast 0%
- MASK In use Measures whether a model contradicts its own elicited beliefs under pressure to lie. Honesty separated from accuracy.
Muse Spark Open 98.1% - 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. GPT-6 Astra 8.50%
- Agentic misalignment suite (Anthropic) In use Agents in simulated company settings face threats or goal conflicts that invite blackmail, leaking or sabotage. Score is the misaligned action rate. Claude Sonnet 4.5 0%