GPT-5.5: OpenAI's frontier model in 2026

GPT-5.5 is OpenAI's general-purpose frontier model as of mid-2026. It ships with a 256K context window, four explicit reasoning levels (low / medium / high / extended) so callers can trade depth for latency and cost, the industry's most stable function-calling and structured-output behavior, and native web search baked into the Responses API. Priced at $5 per million input tokens and $30 per million output tokens, it sits between the cheaper Gemini 3 Pro ($2.50/$10) and the more expensive Claude Opus 4.7 ($15/$75). The case for GPT-5.5: you're building an agent, you need tool calling that doesn't surprise you, you want the broadest plugin ecosystem, and you don't need the 1M-context window the Claude beta provides. The case against: refactor-heavy coding work (Claude Sonnet 4.6 edges it) and tasks that need 500K+ context.

Specs

Best at

• Agent loops — most stable tool-calling and structured-output behavior.
• Reasoning-depth control — pay for extended when needed, low when not.
• Versatile general work — writing, summarization, classification, light coding.
• Real-time research — native search in Responses API.

Where it loses

• Refactor-heavy coding — Claude Sonnet 4.6 edges it.
• 500K+ context — Gemini 3 Pro (1M) and Claude Opus 4.7 (1M beta) hold coherence further.
• Cost-sensitive bulk codegen — DeepSeek V4 Pro is ~5% of the price.

Frequently asked questions