A lot has happened in the last few weeks. I am sure that Open AI’s GPT-6 Astra is top of mind for everyone right now. In particular, thoughts on its performance, the looped transformer/recurrent depth aspects, and rumors that Astra is “hiding” its reasoning trace (i.e., chain of thought). So, in this article, I want to start with some brief impressions of Astra and some thoughts on where all this is headed. Then, I will discuss, in detail, what “looped transformers” are, and how (or rather, if) this relates to hiding chains of thought. Lastly, after covering the basics of the looped transformer, I wanted to highlight some new insights from recent research papers on the topic.

First things first. Before getting into the architecture rumors and related research literature, let me briefly summarize some GPT-6 Astra observations and tidbits. Last week, Open AI’s new GPT-6 Astra was released with a big fanfare. I used it over the past couple of days, and it’s an exceptionally good model, likely the best I’ve used as of this writing. But what, exactly, has it improved, and how? Astra is the best model I’ve used so far, and it’s disproportionately good at 3D rendering and animation tasks (relative to other models). With that, I mean that while it leapfrogs its GPT-5.6 predecessor in practically all categories (writing, math, coding, and more), it especially does so when it comes to graphical demos. We can see this also reflected in the benchmarks. For instance, GPT-6 Astra is really good at math and coding, as shown below. One of the highlights (not shown in the figure) is that Astra also achieves 99.9% on the ARC-AGI-3 benchmark (GPT-5.6 Sol only 7.8%), which measures a mix of solving logic puzzles and generalization. However, the math, coding, and computer use benchmarks are more interesting because they are closer to real-world use.

Coming back to the Artificial Analysis Coding Agent Index v1.4 (lower right in the previous figure), which blends several agentic coding tasks, GPT-6 Astra is clearly at the frontier, but it doesn’t pull ahead by leaps and bounds. This can also be seen in the general Artificial Analysis Intelligence Index shown below, which blends different types of tasks, not just coding tasks. Now, the big advantage of Artificial Analysis benchmarks is that they are independent and thus may be a bit more trustworthy than self-evaluated benchmarks by model developers. The harness setup depends on the benchmark. For example, GDPval-AA and AA-Briefcase use their open-source, minimal Stirrup harness across the different LLMs they compare. In the Intelligence Index v4.2 shown above, Terminal-Bench v2.1 uses Terminus 2, and τ³-Banking uses the τ-Bench harness. The separate Coding Agent Index also compares different coding-agent harnesses. For evaluations that use a shared harness, this makes it more of an apples-to-apples comparison. At the same time, during model training, models are typically developed with one primary harness in mind (and fine-tuned less on other harnesses). Plus, the primary harness is often developed to suit and amplify a model’s strengths. So, some of the agentic evaluations might underestimate how well Astra performs in its primary harness. How much this affects its Intelligence Index score would need to be tested by comparing Astra across harnesses on the same tasks. As a side note, as a colleague recently suggested to me (as also recommended by the Claude Code lead), it’s maybe not a bad idea to delete (/archive) some of your existing AGENTS.md contents and SKILL.md files, as newer LLMs have become more efficient at understanding the prompt and solving the problem at hand. The extra hand-holding could unnecessarily constrain newer models and lead to worse solutions. Of course, I am not suggesting never using SKILL.md files again, but for some workflows, because they can improve efficiency upon reuse, si...