Self-preference bias (Anthropic)
Claude Opus 5.5 0.07 leads since September 2026
Only in system cards Models grade transcripts attributed to themselves or to other models. Measures whether scores favor the model's own outputs.
In-house Anthropic evaluation. The tasks are not public.
- Made by
- Anthropic
- Released
- September 2025
- Kind
- Bias, fairness and politics
- Level
- Everyday
- Scored
- Checked automatically
- Answers
- Open-ended
- Tasks
- Kept private
- Strongest model tested
- Claude Opus 5.5 #4 on the capability index
- Last in a system card
- October 2026
- Last model added
- October 2026
4
Models scored in lab cards
10
System cards report it, from 1 lab
Claude Opus 5.5 leads with 0.07
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 0.07
- 2 Claude Sonnet 5.5 0.16
- 3 Claude Haiku 5.5 0.23
- 4 Claude Opus 4.7 0.40
Source: Labs’ model cards
| # | Model | Score | Setting | Date | Source |
|---|---|---|---|---|---|
| 1 | Claude Opus 5.5 | 0.07 | Sep 2026 | Lab model card | |
| 2 | Claude Sonnet 5.5 | 0.16 | Sep 2026 | Lab model card | |
| 3 | Claude Haiku 5.5 | 0.23 | Oct 2026 | Lab model card | |
| 4 | Claude Opus 4.7 | 0.40 | Apr 2026 | 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
Source: Labs’ model cards
Scores over time
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
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.
10 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 |
|---|---|---|---|---|
| Oct 7, 2026 | Claude Haiku 5.5 system card | 0.23 | Self-preference bias, 0.23 points on a 0 to 9 scale with the Claude system prompt reminder, 0.15 without (6.3.2) | Alignment |
| Sep 28, 2026 | Claude Sonnet 5.5 system card | 0.16 | Self-preference bias, 0.16 points on a 0 to 9 scale when reminded it is Claude (0.06 without the reminder) (6.3.1, Figure 6.3.1.A) | Alignment |
| Sep 22, 2026 | Claude Opus 5.5 system card | 0.07 | Self-preference bias, 0.07 points on a 10-point scale with the Claude-identity system prompt (0.01 with no system prompt) (6.5.3, Figure 6.5.3.A) | Alignment |
| May 28, 2026 | Claude Opus 4.8 system card | Self-preference bias in four prompting conditions on a 10-point scale, chart without printed values. Text says zero is within the error bars in all four (6.3.5, Figure 6.3.5.A) | Alignment | |
| Apr 16, 2026 | Claude Opus 4.7 system card | 0.4 | Self-preference bias, 0.4 on a 10-point scale in the largest condition (Claude system prompt, CoT on), stated in text. Other three conditions chart without printed values (6.3.5, Figure 6.3.5.A) | Alignment |
| Apr 7, 2026 | Claude Mythos Preview system card | Self-recognition bias in transcript grading, four conditions, chart without printed values. Text says an earlier version showed less than 0.1 points on a 10-point scale (4.3.5, Figure 4.3.5.A) | Alignment | |
| Feb 17, 2026 | Claude Sonnet 4.6 system card | Self-preference bias in transcript grading, four conditions, chart without printed values (Figure 4.6.2.A) | Alignment | |
| Feb 5, 2026 | Claude Opus 4.6 system card | Self-preference evaluation, score difference when transcripts are labeled as written by Claude, four conditions, chart without printed values; text says less than 0.2 points on a 10-point scale (Figure 6.3.7.A) | Alignment | |
| Nov 24, 2025 | Claude Opus 4.5 system card | Self-preference evaluation, Benchmark and Poems variants, change in probability of choosing itself, chart without printed values (Figure 6.8.A) | Alignment | |
| Sep 29, 2025 | Claude Sonnet 4.5 system card | Self-preference on decision tasks, Benchmark and Poems variants, increase in probability of choosing itself, chart without printed values (Figure 7.5.9.1.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% - 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%