Model comparison

GPT-5.6 Sol vs GPT-6 Sol

Two OpenAI tiers compared on the figures that decide which one a workload actually needs.

Catalog record checked September 26, 2026Individual provider fields may changeEvidence confidence: High — see receipts below

OpenAI

GPT-5.6 Sol

Frontier

OpenAI

GPT-6 Sol

Balanced

AI model capability comparison
Specification	GPT-5.6 Sol	GPT-6 Sol
Provider
Provider	OpenAI	OpenAI
Tier
Tier	Frontier	Balanced
Context window
Context window	1.05M	1.05M
Max output
Max output	128K	128K
Input / 1M tokens
Input / 1M tokens	$4	Winner: $2
Output / 1M tokens
Output / 1M tokens	$20	Winner: $10
Weights
Weights	Closed	Closed
Parameters
Parameters	previous-generation reasoning + coding model	GPT-6 mid-price tier
Reasoning levels
Reasoning levels	none, low, medium, high, xhigh, max	none, low, medium, high, xhigh, max
Modalities
Modalities	text, image	text, image
API model id
API model id	gpt-5.6-sol	gpt-6-sol
Released
Released	July 9, 2026	September 22, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)
Artificial Analysis Intelligence Index [max] (2026-09-26)	47	Winner: 47.5
Terminal-Bench 2.1 (2026-07-09)
Terminal-Bench 2.1 (2026-07-09)	88.8	Not verifiedUnverified
GPQA Diamond (2026-07-09)
GPQA Diamond (2026-07-09)	94.6	Not verifiedUnverified
DeepSWE 1.1 [max] (2026-09-22)
DeepSWE 1.1 [max] (2026-09-22)	Not verifiedUnverified	68.8
OSWorld 2.0 (offline) [xhigh] (2026-09-22)
OSWorld 2.0 (offline) [xhigh] (2026-09-22)	Not verifiedUnverified	60.5
Terminal-Bench 4.0 [max] (2026-09-26)
Terminal-Bench 4.0 [max] (2026-09-26)	Not verifiedUnverified	43.9

Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

2026-09-26
Artificial Analysis Terminal-Bench 4.0 (independent AA run, part of Intelligence Index v4.3.2)
Agentic terminal work: long multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNOT comparable with Terminal-Bench 2.x or 3.0 — 4.0 uses a new, non-overlapping task set. Within 4.0, scores from different harnesses (tbench.ai agent entries vs Artificial Analysis runs) are not interchangeable.
2026-09-26
Artificial Analysis
Composite index blending reasoning, knowledge, and coding evals into one 0–100 score.
Comparable with caveatOnly same-version scores are comparable. v4.3.2 was rebaselined (the top score fell from 66 on v4.1.1 to ~58), so v4.1.1 figures must not be compared with v4.3.2 figures — check measuredAt.
2026-09-22
OpenAI — Introducing GPT-6 Sol and Luna (vendor)
Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task.
Directly comparable
2026-07-09
OpenAI — GPT-5.6 evals table (vendor)
Agentic terminal work: multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.

Pricing tiers

GPT-5.6 Sol: Launch list was $5/$30; cut to $4/$20 on 2026-08-21, promo held at least through 2026-11-21. Above 272K input the whole request bills 2x input / 1.5x output ($8/$30). Cached input $0.40/MTok; cache writes 1.25x input; batch $2/$10. Knowledge cutoff Feb 16 2026.

GPT-6 Sol: Replaces GPT-5.6 Sol at 50% of its $4/$20 promo price. Cached input $0.20/MTok; cache writes $2.50 (1.25x). Above 272K input the whole request bills $4/$15 ($0.40 cached). Batch/Flex $1/$5; Fast mode $4/$20. Knowledge cutoff Apr 20 2026. Launched in the API, ChatGPT Work and Codex the same day.

FrontierRecord checked September 26, 2026

GPT-5.6 Sol

GPT-5.6 Sol was OpenAI's GPT-5.6 flagship for complex reasoning and coding with a 1.05M-token context — superseded on 2026-09-22 by GPT-6 Sol at half the price.

Best for

Complex reasoning
Agentic coding
Hard knowledge work

Watch out

Superseded: GPT-6 Sol lists $2/$10, half this row's $4/$20 promo rate, and scores higher on the Artificial Analysis index. Still served; 'max' effort and 'ultra' multi-agent mode multiply token use.

BalancedRecord checked September 26, 2026

GPT-6 Sol

GPT-6 Sol brings GPT-6 Astra's training advances to OpenAI's mid-priced tier — OpenAI claims roughly half GPT-5.6 Sol's factual-error rate at half its price, with a 1.05M-token context.

Best for

Default OpenAI production model
Agentic coding
Long-context knowledge work

Watch out

Brand-new (2026-09-22): the DeepSWE figure is vendor-reported and it is not yet on the independent boards; long prompts above 272K bill $4/$15 for the whole request.

When the cheaper one wins

GPT-6 Sol is cheaper on output at $10 per million tokens against $20 for GPT-5.6 Sol — about 2.0×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.

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Evidence confidence: High

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

Pricing verified on both sides — Input and output rates are verified for both models.
5/5 core specs verified on both sides — All core specifications verified for both models.
1 shared named benchmark (scores match) — Measured on: Artificial Analysis Intelligence Index — scores are equivalent, so the benchmark does not separate the pair.
Verified within the last 90 days — Newest catalog check was 2 days ago.
Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

GPT-5.6 Sol: OpenAI — GPT-5.6 (accessed 2026-08-29)
GPT-5.6 Sol: OpenAI API pricing (gpt-5.6-sol $4/$20) (accessed 2026-08-29)
GPT-5.6 Sol: OpenAI — Introducing GPT-6 Sol and Luna (GPT-5.6 Sol successor) (accessed 2026-09-26)
GPT-6 Sol: OpenAI — Introducing GPT-6 Sol and Luna (accessed 2026-09-26)
GPT-6 Sol: OpenAI model docs — gpt-6-sol (1.05M context, 128K output) (accessed 2026-09-26)
GPT-6 Sol: OpenAI API pricing (gpt-6-sol $2/$10, cached $0.20) (accessed 2026-09-26)
GPT-6 Sol: OpenAI API changelog (Sep 22 2026) (accessed 2026-09-26)

Related comparisons

Diving deeper on one model? GPT-5.6 Sol · GPT-6 Sol

Common questions

GPT-5.6 Sol vs GPT-6 Sol

Answered from the verified figures on this page rather than general guidance.

Is GPT-5.6 Sol or GPT-6 Sol cheaper for input?

GPT-6 Sol is cheaper at $2 per million input tokens, against $4 for GPT-5.6 Sol — roughly 2.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.6 Sol has tiered pricing: Launch list was $5/$30; cut to $4/$20 on 2026-08-21, promo held at least through 2026-11-21. Above 272K input the whole request bills 2x input / 1.5x output ($8/$30). Cached input $0.40/MTok; cache writes 1.25x input; batch $2/$10. Knowledge cutoff Feb 16 2026. GPT-6 Sol has tiered pricing: Replaces GPT-5.6 Sol at 50% of its $4/$20 promo price. Cached input $0.20/MTok; cache writes $2.50 (1.25x). Above 272K input the whole request bills $4/$15 ($0.40 cached). Batch/Flex $1/$5; Fast mode $4/$20. Knowledge cutoff Apr 20 2026. Launched in the API, ChatGPT Work and Codex the same day.

Is GPT-5.6 Sol or GPT-6 Sol cheaper for output?

GPT-6 Sol is cheaper at $10 per million output tokens, against $20 for GPT-5.6 Sol — roughly 2.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.6 Sol has tiered pricing: Launch list was $5/$30; cut to $4/$20 on 2026-08-21, promo held at least through 2026-11-21. Above 272K input the whole request bills 2x input / 1.5x output ($8/$30). Cached input $0.40/MTok; cache writes 1.25x input; batch $2/$10. Knowledge cutoff Feb 16 2026. GPT-6 Sol has tiered pricing: Replaces GPT-5.6 Sol at 50% of its $4/$20 promo price. Cached input $0.20/MTok; cache writes $2.50 (1.25x). Above 272K input the whole request bills $4/$15 ($0.40 cached). Batch/Flex $1/$5; Fast mode $4/$20. Knowledge cutoff Apr 20 2026. Launched in the API, ChatGPT Work and Codex the same day.

Which has the larger context window, GPT-5.6 Sol or GPT-6 Sol?

Both accept about 1.05M tokens of context, so document length will not decide between them.

Do GPT-5.6 Sol and GPT-6 Sol support the same reasoning levels?

Yes — both accept the same effort settings: "none", "low", "medium", "high", "xhigh", "max". Higher effort costs more and takes longer, so start low and raise it only where output quality actually improves.

Should I use GPT-5.6 Sol or GPT-6 Sol?

GPT-5.6 Sol is the frontier tier and GPT-6 Sol the balanced tier. The useful question is whether your hardest task actually fails on the cheaper one — most production volume such as classification, extraction and summarisation does not.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

Input price: GPT-6 Sol costs $2 per 1M tokens versus $4 for GPT-5.6 Sol — a 2x difference at the headline tier.
Measured capability: GPT-6 Sol leads Artificial Analysis Intelligence Index 47.5 to 47 (measured 2026-09-26).
Positioning: GPT-5.6 Sol sits in the frontier tier, GPT-6 Sol in the balanced tier — most production volume (classification, extraction, summarisation) does not need the pricier tier.

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