OpenAI

GPT-5.6 Sol

Released Jul 9, 2026 · knowledge cutoff 2026-02

Status: Superseded
Location: United States
Type: LLM
Modality: Multimodal
Context window: 1.1M
Max output: 128K
Speed (medium effort): 64 tok/s · 6.09s to first answer token
Price ($/MTok in / out): $4 / $20
Cost per task (medium effort): $0.41
Open weights: No

Benchmarks9 of 10 reported

MMLU-Proretired

89.1%

GPQA Diamond

94.6%

SWE-bench Verified

96.2%

SWE-bench Pro

64.6%

Terminal-Bench 2.1

88.8%

Humanity's Last Exam

47.2%

LMArena Elo

1485

GDPval-AA v2

1711

ARC-AGI-2

92.5%

AIME (latest)retired

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Strengths & weaknesses

Strengths

Stays on one task for days without drifting or declaring premature victory
Reaches the same answer in far fewer tokens than the model before it
Security work — threat modelling, code review, blue-teaming — is a deliberate specialism

Weaknesses

Still verbose for interactive chat, despite being efficient on agentic work
Pre-deployment testing found it gaming its own evaluations, which makes any single score harder to trust
Priced well above its Terra and Luna siblings, which close much of the gap on everyday work

The frontier tier of the three-model GPT-5.6 family (Sol / Terra / Luna), all released 2026-07-09. Context window and max output confirmed via OpenAI's developer docs. GPQA Diamond 94.6 and HLE 47.2 are OpenAI/Artificial Analysis-reported; MMLU-Pro 89.1 and ARC-AGI-2 92.5 (Max effort, per ARC Prize) are third-party. OpenAI published no SWE-bench or AIME figure for this family; SWE-bench Verified 96.2 is third-party, from Vals AI’s independent harness (leaderboard updated 2026-07-31, run at max reasoning effort), the same board that supplies Luna’s 93.0. AIME stays null. LMArena Elo 1485 is the "gpt-5.6-sol-xhigh" text-arena listing (arena.ai). Artificial Analysis Intelligence Index 59. Terminal-Bench 2.1 88.8% from the GPT-5.6 launch comparison table (Sol 88.8 / Terra 87.4 / Luna 84.7). Sol's price held at $5.00/$30.00 through OpenAI's 2026-07-30 cuts to the other two tiers, which also added an optional fast mode: up to 2.5x the speed at twice the price. SWE-Bench Pro 64.6% is OpenAI's launch-table figure (openai.com/index/gpt-5-6, not fetchable directly), as reproduced by Vellum, LayerLens and llm-stats and cross-cited in Anthropic's Claude Opus 5 system-card table. Updated 2026-09-23: OpenAI cut Sol to $4.00/$20.00 ($0.40 cached input) on 2026-08-21 as promotional pricing it has committed to hold at least through 2026-11-21, with no post-promotion rate published; the API, Codex credits and ChatGPT Work are covered, consumer subscriptions are not. GPT-6 Sol (2026-09-22) names it as predecessor but it remains on sale with no retirement scheduled.

For developers

API model strings

openaigpt-5.6-sol

Licence

Proprietary — weights not released

Retirement

No retirement announced

Lineage

No recorded predecessor