Claude Fable 5.1 vs Grok Build 0.1

Anthropic's most capable generally available model, sitting above the Opus line. Fable 5.1 is built for long, unsupervised work: multi-day coding, agentic research, and tasks that run across dozens of tool calls. It reads text and images, maintains a very large context, and reasons before every answer at an adjustable depth. Its knowledge is the most recent of any Claude model. Anthropic positions Opus 5 as the starting point for most work, and Fable 5.1 for teams whose evaluations demand a higher ceiling.

xAI's coding model, purpose-built for autonomous software engineering rather than chat. Grok Build 0.1 acts as an engineering agent: it reasons through a problem, writes code, runs your terminal, checks for errors, and fixes its own mistakes in a loop. It reads text and images, always reasons before answering, and natively supports Model Context Protocol. Built for long-horizon coding that runs with little supervision, at a low cost, tuned for agent loops.