Claude Opus 5.5 and GPT-6 Sol launched September 22, 2026, with different pricing models and performance characteristics. While GPT-6 Sol has lower per-token costs, the true comparison requires analyzing cost per completed task, accounting for token efficiency, retry rates, cache usage, and success rates. Opus 5.5 shows stronger benchmark scores but does not always justify its price premium on short deterministic tasks.
This guide explains how to work effectively with Opus 5.5 in Claude and Claude Code. Key practices include giving complete tasks with clear finish lines, removing explicit thinking prompts since Opus 5.5 thinks automatically, sending follow-ups during long runs, specifying design patterns to avoid, and setting rules in CLAUDE.md about when to stop for input versus continuing autonomously.
Documentation updates for Claude Opus 5.5 model, changing API references from claude-opus-5 to claude-opus-5-5 across Swift SDK examples and model identifier constants.