GPT-5.5 is OpenAI’s April 2026 flagship, the model that finally merged the separate reasoning (o-series) and chat lines into one system. Its standout strength is terminal-native agentic work: on Terminal-Bench 2.0 it leads the field, making it the default choice for Codex CLI agents and long-running automated tasks.
It is also natively omnimodal — unlike most rivals it accepts audio and video as input, not just text and images. A faster Instant default and a higher-accuracy GPT-5.5 Pro round out the tier.
The trade-offs are price and context: output tokens are the most expensive of the closed frontier ($30/1M), and the Codex context window (400K) is smaller than Claude’s or Gemini’s 1M, though the API exposes up to 1M.
Successor: OpenAI announced GPT-5.6 on June 26, 2026 — a tiered family (Sol / Terra / Luna). Flagship Sol holds GPT-5.5’s $5/$30 price while pushing agentic scores higher, and the new Terra and Luna tiers undercut GPT-5.5 on price for everyday and high-volume work. GPT-5.6 launched in a limited preview; GPT-5.5 remains the broadly available default for now.
Best for
- Autonomous coding agents and Codex CLI workflows
- Multi-hour, long-horizon automated runs
- Multimodal assistants
Pros & cons
Strengths
- Best-in-class for terminal/CLI agents (Terminal-Bench 2.0 ≈ 82.7%)
- Natively omnimodal — accepts audio and video input
- Folded the o-series and Codex lines into one model
Limitations
- Highest output price of the closed frontier
- Default context smaller than Claude/Gemini outside the API