GPT-5.6 Sol

OpenAI

OpenAI's flagship in the GPT-5.6 generation (released July 2026), for the hardest problems including complex coding and security research. Sol set a new state of the art on Terminal-Bench 2.1, with an 'ultra' subagent mode for the hardest command-line tasks. GPT-5.6 fixes three tiers - Sol, Terra, Luna - and floats the generation number, signaling more frequent capability upgrades.

Strengths

GPT-5.6 flagship for the hardest coding and security-research tasks
State-of-the-art on Terminal-Bench 2.1 (with an 'ultra' subagent mode for the hardest tasks)
Part of a reset Sol/Terra/Luna tiering with a floating generation number
More predictable prompt caching with explicit cache breakpoints

Caveats

Limited preview as of June 2026 - not yet generally available
Context window not finalized at preview (reported up to ~1.5M, unconfirmed)
Premium flagship pricing at $5/$30 per 1M tokens

Vendor: OpenAI
Context Window: 1,050,000 tokens
Max Output: 128,000 tokens
License: Proprietary
Release Date: 2026-07-09
Training Cutoff: 2026-02-16
Modalities: text
image

Capabilities

Vision

Audio

Video

Tool Use

Resources

API Documentation

Pricing

$5 per 1M input tokens, $30 per 1M output tokens. Launch pricing; check OpenAI's pricing page for current rates.