Claude Opus 4.8
29 values about Claude Opus 4.8 from 4 documents, in 8 metric families. In each family, values from its own document come first.
- Developer
- Anthropic
- Release date
- 28 May 2026The date of its first card in the dataset, the Claude Opus 4.8 System Card.
- Availability
- Public
- Its own document
- Claude Opus 4.8 System Card · 28 May 2026
- Also reported in
- Claude Fable 5 & Claude Mythos 5 System Card · 9 Jun 2026
- Claude Sonnet 5 System Card · 30 Jun 2026
- Claude Opus 5 System Card · 24 Jul 2026
Data as of 26 Sep 2026 · Dataset v0.1 · Methodology v0.1 · Changelog
Values by metric family
Each value as the document printed it. Select a value for its source, its checks and its history. Values from other documents are listed after the model’s own, each marked as the first report of that measure or as a restatement.
KeyVerifiedUnverifiedDisputedCorrected read off a figure or stated in wordsA value opens its source and history.
M1 · Evaluation awareness 2 values
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| Unverbalized grader awarenessShare of cases with grader awareness | Claude Opus 4.8 System Card28 May 2026 | |
| Verbalized grader speculationShare of training episodesCondition: RL training | Claude Opus 4.8 System Card28 May 2026 | |
M3 · Sabotage and sandbagging 1 value
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| SHADE-Arena / Minimal-LinuxBenchStealth success vs peers | Claude Opus 4.8 System Card28 May 2026 | |
M4 · Misalignment audits 1 value
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| Refusal to assist AI safety R&DRefusal rate | Claude Opus 4.8 System Card28 May 2026 | |
M5 · Honesty and hallucination 3 values
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| Agentic code summary honestyFailure to report important events | Claude Opus 4.8 System Card28 May 2026 | |
| Input hallucinationRate of hallucinating missing reference | Claude Opus 4.8 System Card28 May 2026 | |
| Input hallucinationRate of hallucinating unavailable tool | Claude Opus 4.8 System Card28 May 2026 | |
M7 · Harmful compliance and over-refusal 8 values
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| Single-turn benign requestsOver-refusal rateCondition: claude.ai system prompt | Claude Opus 4.8 System Card28 May 2026 | |
| Single-turn benign requestsOver-refusal rateCondition: no system prompt; API | Claude Opus 4.8 System Card28 May 2026 | |
| Single-turn violative requestsHarmless response rateCondition: claude.ai system prompt | Claude Opus 4.8 System Card28 May 2026 | |
| Single-turn violative requestsHarmless response rateCondition: no system prompt; APIRestated later: compare with the later value | Claude Opus 4.8 System Card28 May 2026Restated later: compare with the later value | |
| From other documents | ||
| Malicious Claude Code useRefusal rate, malicious requestsClaude Sonnet 5 System Card30 Jun 2026First reported | Claude Sonnet 5 System Card30 Jun 2026First reported | |
| Malicious computer useRefusal rateClaude Sonnet 5 System Card30 Jun 2026First reported | Claude Sonnet 5 System Card30 Jun 2026First reported | |
| Single-turn violative requestsHarmless response rateCondition: no system prompt; APIClaude Sonnet 5 System Card30 Jun 2026Restated: compare with the earlier value | Claude Sonnet 5 System Card30 Jun 2026Restated: compare with the earlier value | |
| Single-turn violative requestsHarmless response rateCondition: no system prompt; APIClaude Opus 5 System Card24 Jul 2026Restated: compare with the earlier value | Claude Opus 5 System Card24 Jul 2026Restated: compare with the earlier value | |
M9 · Prompt injection 2 values
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| Indirect prompt injection (external benchmark)Attack success rate | Claude Opus 4.8 System Card28 May 2026 | |
| From other documents | ||
| Indirect prompt injection (ART-style)Attacker success within 15 attemptsClaude Opus 5 System Card24 Jul 2026First reported | Claude Opus 5 System Card24 Jul 2026First reported | |
M10 · Dangerous capabilities and risk determinations 11 values
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| Anthropic ECI (AECI)Capability index | Claude Opus 4.8 System Card28 May 2026 | |
| Autonomy threat model 2 (automated R&D)RSP determination | Claude Opus 4.8 System Card28 May 2026 | |
| CB-2 threat modelRSP determination | Claude Opus 4.8 System Card28 May 2026 | |
| CyberGymTargeted vuln reproduction rate | Claude Opus 4.8 System Card28 May 2026 | |
| CyberGymTargeted vuln reproduction rateCondition: with safeguards | Claude Opus 4.8 System Card28 May 2026 | |
| ExploitBenchMean flags capturedCondition: AutoNudge arm | Claude Opus 4.8 System Card28 May 2026 | |
| Firefox 147 exploitationFull exploit rateCondition: without safeguards | Claude Opus 4.8 System Card28 May 2026 | |
| Long-form virology task 1Score | Claude Opus 4.8 System Card28 May 2026 | |
| Long-form virology task 2Score | Claude Opus 4.8 System Card28 May 2026 | |
| Multimodal virology (VCT)Score | Claude Opus 4.8 System Card28 May 2026 | |
| From other documents | ||
| AI R&D LLM training taskAverage speedupCondition: re-runClaude Fable 5 & Claude Mythos 5 System Card9 Jun 2026First reported | Claude Fable 5 & Claude Mythos 5 System Card9 Jun 2026First reported | |
M12 · Chain-of-thought monitorability 1 value
| Evaluation and metric | Value | Document |
|---|---|---|
| From its own documentClaude Opus 4.8 System Card · 28 May 2026 | ||
| Accidental CoT supervision in RLShare of training episodes affected | Claude Opus 4.8 System Card28 May 2026 | |
Restated in later documents
A later document reported values about Claude Opus 4.8 again. Each pair is shown side by side: both values are kept with their own documents, and the later one does not replace the earlier.
| Earlier value | Later value |
|---|---|
| M7 · Harmful compliance and over-refusal | |
| Single-turn violative requestsHarmless response rateCondition: no system prompt; API | |
| Claude Opus 4.8 System Card28 May 2026 · its own document | Claude Sonnet 5 System Card30 Jun 2026No reason stated |
| Single-turn violative requestsHarmless response rateCondition: no system prompt; API | |
| Claude Opus 4.8 System Card28 May 2026 · its own document | Claude Opus 5 System Card24 Jul 2026No reason stated |
Risk determinations
The developer's formal decisions about Claude Opus 4.8 under its framework, as printed. Levels from different frameworks do not map onto one another.
| Domain | Level as printed | Framework and document |
|---|---|---|
| Bio/chem | not beyond Mythos Preview Responsible Scaling Policy Claude Opus 4.8 System Card · 28 May 2026 | Responsible Scaling Policy Claude Opus 4.8 System Card · 28 May 2026 |
| AI R&D / autonomy | not applicable Responsible Scaling Policy Claude Opus 4.8 System Card · 28 May 2026 | Responsible Scaling Policy Claude Opus 4.8 System Card · 28 May 2026 |
Revisions
Changes made to a document after it was published that change a value about Claude Opus 4.8.
0.890.90Explained — The changelog lists the corrected score.
New value:
How we know Old and new text as the source registry quotes the changelog entry of 17 Jun 2026; v0 row 350 records the corrected value. The changelog has not been re-read by us, so the revision is unverified.
Checked Not yet checked
No copy of the 3 Jun 2026 version held No copy of the 17 Jun 2026 version held