GPT-5.6 MCP: Testing Servers With Sol, Terra & Luna

Short summary

OpenAI released GPT-5.6 on July 9, 2026 in three tiers — Sol (flagship), Terra (balanced), and Luna (cheapest) — all with 1M-token context, 128K output, and native MCP support via the Responses API. Programmatic Tool Calling batches tool logic into a single JavaScript sandbox script, cutting tokens 38–63.5% on real workloads. The author recommends starting on Luna for simple reads, escalating to Terra for multi-step agents, and reserving Sol for complex multi-server chains.

• •GPT-5.6 ships in three tiers (Sol, Terra, Luna) with shared 1M context and native MCP support
• •Programmatic Tool Calling reduces token usage 38–63.5% by batching tool calls in a V8 sandbox
• •Start on Luna, escalate to Terra, reserve Sol for hard multi-server agentic chains

Generated with AI, which can make mistakes.