AI developer tools · What shipped

Anthropic released Claude Fable 5.1 and Claude Mythos 5.1, with Fable 5.1 now generally available. Fable 5.1 costs approximately 25% less than Fable 5 for typical workloads and up to 45% less for highly agentic work, achieved through 75% reduced pricing on cache reads. The model shows performance improvements across multiple benchmarks: Terminal-Bench-Science 0.1 (52.6% vs 24.7%), Terminal-Bench 4.0 (55.8% vs 42.0%), CursorBench 3.2.0 (73.4% vs 70.5%), and Humanity's Last Exam (65.0% with tools vs 63.8% for Fable 5), while maintaining reduced false positives in cybersecurity safeguards (60% fewer than previous versions). Claude Mythos 5.1, restricted to vetted organizations, demonstrated advanced scientific capabilities including designing protein binders with hit rates near 50% (compared to typical 10-15%), creating high-resolution Venus elevation maps, and optimizing GPU kernels for deep learning models with up to 2.5x speedups.

Inception Labs released Mercury 2.5, a diffusion-based language model offering 40% improvement in intelligence over Mercury 2 while maintaining low latency and cost. The model achieves 1,107 tokens per second on NVIDIA GPUs, supports 260K context length, and is priced at $0.20 per million input tokens and $0.75 per million output tokens (80% discount at launch: $0.04/$0.15). Mercury 2.5 is positioned as comparable to cost-optimized frontier models like GPT-4o mini and Claude Haiku, with production deployments across search agents, voice applications (170ms time-to-first-token), and coding assistants. The company also previewed Mercury Voice and Mercury Router, with the latter routing requests across open and closed models for optimal quality-speed-cost tradeoffs. Mercury 2.5 is available through Inception API, Baseten, and OpenRouter with enterprise deployment options.

Visual Studio 2026 is integrating AI-assisted C++ workflows combining C++-specific code understanding with GitHub Copilot for code navigation, modernization, refactoring, debugging, and performance optimization. MSVC Build Tools v14.52, shipping November 2026, will include the /std:c++23 switch and achieve C++23 completeness, with constexpr cmath implementation available as an experimental opt-in feature. Copilot CLI, built on the modern Copilot SDK shared with Visual Studio and VS Code, now supports a C++ language server plugin for richer code navigation, diagnostics, and semantic intelligence, moving beyond grep-style searches in terminal workflows.