Based on the tokenizer data the new stealth model "space-bunny-alpha" appears to likely be part of MiniMax lineage. xitter.cf/OpsConfig/status/21029…

Back when they supported fine-tuning distillation was a celebrated feature of the API: (granted they only ever supported distilling from one OpenAI model to another. )

While regardless of chess performance Anthropic models have continued to get stronger in other domains, my own anecdotal experience was that Opus 4.5 and Opus 4.6 were the last Opus models to feel consistent. Ever since Opus 4.7 I feel like I am constantly having to correct and double-check the model's work. One moment the model feels smart, the next it is apologizing to me for the umpteenth time for having made a mistake. These days anytime I use an Anthropic model for any serious work I am constantly farming out adversarial reviews to codex/OpenAI models. This change in anecdotal vibes for me coincided with Anthropic's shift to "adaptive thinking". The older model's used the now deprecated "extended thinking" feature. If we add in data on the older model's we see a profile far closer to the OpenAI models as far as thinking token allocation. Adaptive thinking definitely saves money on a per API call basis, but I do wonder to what extent that comes at the cost of quality. 8/

Another way of parsing thinking token data is to not look just at when zero tokens are used, but to bucket the distribution of thinking tokens across different reasoning effort levels. 7/

Anthropic defines their model's reasoning behavior as: 5/

One of the first things that caught my eye when poking though the data from hundreds of Anthropic model chess games was how these models allocate reasoning/thinking tokens. In particular, how often an Anthropic model will respond without generating any thinking tokens when playing chess. 3/

Out of curiosity, I ran it through my standard chess eval gauntlet on low, medium, high, and max. It lost every game except one. Here is one of its losses, mate in 7 moves with stockfish at 1320. All match replays have been added to the library: codeandstream.com/chess/#g=s…

Based on the tokenizer data the new stealth model "space-bunny-alpha" appears to likely be part of MiniMax lineage.

Just to make sure I understand are saying you aren't sure if they had these settings turned on/off, which seems quite reasonable? Or are you saying even if these settings are turned off there is still some gray area?

As much fun as it is to have LLMs play against stockfish, sometimes it's nice to watch some 1v1 matches. Twenty games of GPT-6 Astra versus Fable 5.1 are now up on: codeandstream.com/chess