Differences Between Claude Opus 4.8 and Claude Fable 5 on MineBench

**Some Notes:** * *Average Inference Time: 18m 04s (1,084.4s)* * Faster than Claude 4.8 Opus, which averaged 24m 48s / 1,487.9 seconds * Surprising since in the [Claude.ai](http://Claude.ai) web harness, Fable feels like it thinks for much longer, but through the API it averaged less total time than Opus 4.8 did * *Total Cost (for 15 builds): $54.93* * More expensive than Opus 4.8, which was $41.52 for the same 15 builds * Considering Fable’s API pricing is 2x more than Opus 4.8’s, the MineBench cost was only about 30% higher * Fable is producing fewer total tokens overall it seems, which is likely contributing to the lower cost Furthermore, I think the quality of the model's builds was very surprising: they don't seem as big of a leap over GPT 5.5 Pro as the the [official benchmark scores might suggest](https://www.anthropic.com/_next/image?url=https%3A%2F%2Fwww-cdn.anthropic.com%2Fimages%2F4zrzovbb%2Fwebsite%2F1e65982497d7d4891219ed0e83141625a291b860-2600x2870.png&w=3840&q=75), but the model clearly has very high attention to detail. For example, this is the first model that in the Arcade Machine build, actually created a correctly detailed screen (of PacMan), including the full layout, a score, and even a "1UP" label. Though it seems the model was quite conservative with its interpretation of the system-prompt, and (subjectively) not *all* of its builds were clearly more impressive than 4.8. Still, the results were quite surprising, so I reached out to the [VoxelBench](https://voxelbench.ai/) team, who also confirmed in their tests the builds were of generally much smaller size. They mentioned adding these two lines to the template produced much better builds in their case: LEVEL OF DETAIL: MAXIMUM BOUNDING BOX: UNLIMITED Though I'm not changing the MineBench system-prompt to cater to any specific models, I do think it's worth noting that one might be able to achieve much better results with improved prompting. It's also interesting how the model was able to make these detailed builds while keeping the overall JSON size lower in comparison to Opus 4.8, and while thinking for less time. Pure speculation: I think this might indicate why Claude Fable is supposedly much better at coding-related tasks; it actually completes the task with an intuitive approach and without adding excess. * Full release-notes/thoughts on the [GitHub release](https://github.com/Ammaar-Alam/minebench/releases/tag/3.7.0) * **If you enjoy these posts please feel free to help** [**fund**](https://buymeacoffee.com/ammaaralam) **the benchmark** **Benchmark:** [https://minebench.ai/](https://minebench.ai/) **Git** **Repository:** [https://github.com/Ammaar-Alam/minebench](https://github.com/Ammaar-Alam/minebench) **Previous Posts:** * [Comparing Opus 4.7 and Opus 4.8](https://www.reddit.com/r/ClaudeAI/comments/1tt3a8h/differences_between_opus_47_and_opus_48_on/) * [Comparing GPT 5.4 and GPT 5.5](https://www.reddit.com/r/singularity/comments/1sxapqb/differences_between_gpt_54_and_gpt_55_on_minebench/) * [Comparing Kimi K2.5 and Kimi K2.6](https://www.reddit.com/r/LocalLLaMA/comments/1srs4uj/differences_between_kimi_k25_and_kimi_k26_on/) * [Comparing Opus 4.6 and Opus 4.7](https://www.reddit.com/r/ClaudeAI/comments/1sofgno/differences_between_opus_46_and_opus_47_on/) * [Comparing GPT 5.4 and GPT 5.4-Pro](https://www.reddit.com/r/OpenAI/comments/1rr0vi4/differences_between_gpt_54_and_gpt_54pro_on/) * [Comparing GPT 5.2 and GPT 5.4](https://www.reddit.com/r/singularity/comments/1rluvdz/difference_between_gpt_52_and_gpt_54_on_minebench/) * [Comparing GPT 5.2 and GPT 5.3-Codex](https://www.reddit.com/r/OpenAI/comments/1rdwau3/gpt_52_versus_gpt_53codex_on_minebench/) * [Comparing Opus 4.5 and 4.6, also answered some questions about the benchmark](https://www.reddit.com/r/ClaudeAI/comments/1qx3war/difference_between_opus_46_and_opus_45_on_my_3d/) * [Comparing Opus 4.6 and GPT-5.2 Pro](https://www.reddit.com/r/OpenAI/comments/1r3v8sd/difference_between_opus_46_and_gpt52_pro_on_a/) * [Comparing Gemini 3.0 and Gemini 3.1](https://www.reddit.com/r/singularity/comments/1ra6x6n/fixed_difference_between_gemini_30_pro_and_gemini/) **Extra Information (if you're confused):** Essentially it's a benchmark that tests how well a model can create a 3D Minecraft like structure. So the models are given a palette of blocks (think of them like legos) and a prompt of what to build, so like the first prompt you see in the post was a fighter jet. Then the models had to build a fighter jet by returning a JSON in which they gave the coordinate of each block/lego (x, y, z). It's interesting to see which model is able to create a better 3D representation of the given prompt. The smarter models tend to design much more detailed and intricate builds. The repository readme might provide might help give a better understanding. *(Disclaimer: This is a public benchmark I created, so technically self-promotion* : )