OpenAI: GPT-5.1-Codex-Max API Price, Cost Calculator & Specs

This is one of the best coding models on the market, period. The GPT-5.1-Codex-Max combines top-tier programming intelligence with serious cost efficiency—at $1.25/$10 per 1M tokens, you're getting near-Sonnet-level coding quality for a fraction of the price. The 400K context window is the real killer feature: it can hold entire enterprise codebases, multiple microservices, and complex documentation simultaneously. That's the kind of horsepower that used to cost $15-20/1M tokens.

Best For:

Enterprise Codebase Projects: Build your AI coding assistant around this as the primary engine. The 400K context means it can understand complex system architecture across dozens of files, handle multi-service refactors, and maintain consistency across large teams. Way cheaper than Claude Sonnet for this use case.

Full-Stack Feature Development: The agentic training makes it exceptional at understanding project context and writing cohesive code across frontend, backend, and database layers. Use it as your main development workhorse for complex features that touch multiple systems.

Codebase Migration Projects: Massive legacy-to-modernization efforts, framework upgrades, or tech stack transitions. The context window is large enough to hold entire file trees plus documentation, letting it understand dependencies and suggest proper migration paths.

Complex Bug Resolution: When you need to trace through complex issues spanning multiple services or modules. The model's ability to maintain context across large codebases makes it invaluable for debugging systems that smaller models can't fully grasp.

AI Development Platform Backend: If you're building GitHub Copilot, CodeT5, orCursor-style products, this hits the sweet spot of coding intelligence and margins. You can actually charge $30-50/month and still maintain healthy gross margins with this model as your core engine.