Both models share a $5 input price, so the comparison starts with output cost: GPT-5.6 Sol at $30 per million output tokens versus Claude Opus 4.8 at $25. GPT-5.6 Sol leads on every Artificial Analysis benchmark: Intelligence Index 58.9 vs 55.7, Coding Index 77.4 vs 74.3, and Agentic Index 54.0 vs 47.2. The agentic gap is the most meaningful, since it is where Sol earns its higher price on multi-step runs with tool calling and execution loops.
Claude Opus 4.8 has been in production since May 2026 and has more real-world evaluation data than Sol's July 9 launch date allows. Teams using it on contract analysis, long-document summarization, and structured output generation report consistent accuracy with a low hallucination rate. GPT-5.6 Sol ships as part of a three-tier family (Sol, Terra, Luna), so routing to a cheaper tier for lower-stakes steps is built into the provider, which simplifies multi-tier routing for OpenAI shops.
Put GPT-5.6 Sol on the steps where the agentic and coding benchmark leads matter: multi-step code generation, command-line agent loops, and tool-calling chains where mid-run failures are expensive. Put Claude Opus 4.8 on the steps where structured output accuracy and a longer production track record are the deciding factors. The $5 output price difference per million tokens means Claude Opus 4.8 is the better default on every step where both models would produce equivalent output.