Anthropic released Claude Fable 5.2 on 9 November. The same day, two external evaluators, Artificial Analysis and Epoch AI, posted their own results on X. The Artificial Analysis Intelligence Index combines nine benchmarks covering areas such as coding, scientific reasoning and knowledge work.

Fable 5.2 scored 65 on the index at its highest reasoning effort (max). Reasoning effort sets how much the model may think before answering, and Fable has five levels. The nearest other models were Gemini 4 Carbon (60) and Claude Opus 5.5 (59).

Artificial Analysis said the lead comes from scientific reasoning, knowledge and coding. The model led five of the nine benchmarks. In Artificial Analysis’s tests it scored 80 per cent on the HLE-Diamond reasoning benchmark (previous best 69 per cent), 73 per cent on Terminal-Bench-Science research tasks (65 per cent) and 49 per cent on the software development benchmark FrontierCode 2.0 (46 per cent). Anthropic’s own results on the last two were almost identical: 74.6 and 49.1 per cent.

The model did not lead every benchmark. On the AA-Briefcase knowledge-work benchmark, its 1,785 Elo points fall within the confidence interval of Opus 5.5’s score (1,800). On the Terminal-Bench 4.0 coding benchmark, it scored 60 per cent at max reasoning effort, the same as Opus 5.5, and trailed models such as Kimi K3.1 Pro (67 per cent).

The tests used the fallback model that Anthropic provides by default. Fable’s safety classifier blocks most cybersecurity tasks, among other things, Anthropic said. In those cases an older Opus model answers the query.

The top score is costly and slow

At max reasoning effort, one index task cost $26.54 on average. Artificial Analysis said that is about 2.6 times the cost of Opus 5.5 and about twice that of Fable 5.1, even though the per-token price fell 20 per cent from the predecessor. The model generated 275 million tokens during the index run, against a median of 72.8 million for models in the same price class. A task took 46.4 minutes on average (median 12.7).

At high and xhigh effort, Fable 5.2 scored 62, more than any other model at any level. At lower levels it can outperform Opus 5.5 while still costing less per task, Artificial Analysis said. The table shows index scores and cost and time per task.

Source: Artificial Analysis, Intelligence Index v5.0.1. Averages per index task; – = not published.

Gemini 4 Carbon was measured at high effort, Opus 5.5 and Fable 5.1 at max.

Epoch: new record, wide uncertainty

Epoch AI said Fable 5.2 raised the record on the Epoch Capabilities Index to 174. The previous record was GPT-6 Astra’s 169. The score exceeds what the trend for reasoning models before GPT-6 Astra would have predicted, Epoch said. In the chart Epoch published, however, the score’s 90 per cent uncertainty interval reaches into the trend’s prediction interval. Epoch tested the model before release using only its own benchmarks. The figure may change.

Fable 5.2 is available on Anthropic’s Claude Platform as claude-fable-5-2 and through AWS, Google Cloud and Microsoft Azure. It costs $8 per 1 million input tokens and $40 per 1 million output tokens. Anthropic recommends starting most coding and knowledge work with Opus 5.5.