GPT-6 Sol vs GPT-5.6 Sol: Half the Price, What Changed
Updated 2026-10-08
Short answer: GPT-6 Sol is the newer, cheaper model and the better default for coding and agent work; GPT-5.6 Sol still wins several legal, finance and competition-programming benchmarks. GPT-6 Sol (released September 22, 2026) costs $2 per million input tokens and $10 per million output – exactly half of GPT-5.6 Sol's $4 and $20. Both have a context window of about 1.05 million tokens.
If you are choosing today, also look at GPT-6.1 Sol, the September 29 update of GPT-6 Sol at the same price – see GPT Sol 6.1 explained.
GPT-6 Sol vs GPT-5.6 Sol at a glance
| GPT-6 Sol | GPT-5.6 Sol | |
|---|---|---|
| Released | September 22, 2026 | July 9, 2026 |
| Input price per 1M (≤272K context) | $2 | $4 |
| Output price per 1M (≤272K context) | $10 | $20 |
| Input / output above 272K context | $4 / $15 | $8 / $30 |
| Cache read per 1M | $0.20 | $0.40 |
| Context window | 1,050,000 tokens | 1,050,000 tokens |
| Knowledge cutoff | April 20, 2026 | February 16, 2026 |
Prices are OpenAI's standard API rates as listed on September 22, 2026 (compiled by gradually.ai). Batch, flex and priority tiers differ.
Benchmarks: what improved and what didn't
Vals AI tested both models on the same 21 benchmark series (data as of late September 2026). The pattern is clear: GPT-6 Sol gained on coding and terminal work, and lost ground on some professional-knowledge tasks.
GPT-6 Sol wins:
- Terminal-Bench 4.0: 34.3% vs 27.8%
- Terminal-Bench Science: 31.4% vs 12.9%
- Code Migration: 57.2% vs 52.9%
- BioMysteryBench: 74.8% vs 71.1%
- MedCode: 47.1% vs 44.0%
- CyberBench 1.1: 78.0% vs 76.3%
GPT-5.6 Sol wins:
- IOI (competition programming): 91.2% vs 82.6%
- Legal Research Bench (all-pass): 48.1% vs 28.8%
- Tax Agent Bench: 68.0% vs 53.0%
- Finance Agent v2: 53.8% vs 49.1%
- Public Benefits Bench: 66.5% vs 56.6%
- Terminal-Bench 2.1: 85.8% vs 83.1%
So "newer" isn't automatically "better at everything". If your product does legal research, tax or finance analysis, test both before switching.
Price: what half the cost means
A task that reads 200,000 tokens and writes 20,000 (under the 272K tier):
- GPT-6 Sol: 0.2 × $2 + 0.02 × $10 = $0.60
- GPT-5.6 Sol: 0.2 × $4 + 0.02 × $20 = $1.20
Long prompts above 272K tokens cost more on both, but GPT-6 Sol stays about half the price. Cached reads drop from $0.40 to $0.20 per million.
Should you upgrade from GPT-5.6 Sol?
Upgrade (to GPT-6 Sol or 6.1 Sol) if:
- You run coding agents, migrations or terminal workflows – the biggest gains are there.
- Cost per task matters; the 2x price cut applies across the board.
- You need fresher knowledge (April vs February 2026 cutoff).
Keep GPT-5.6 Sol for now if:
- Your workload is legal research, tax, finance or benefits questions where 5.6 Sol scored higher, and your own tests confirm it.
- You have prompts tuned for 5.6 Sol and no budget pressure – but plan a re-test, as older models get retired.
How to compare them on your own work
- Take 20–50 real tasks from your product.
- Run both models with identical prompts, tools and effort settings.
- Record pass rate, tokens and time.
- Compare cost per solved task, not per token.
- Repeat when GPT-6.1 Sol or later point releases ship.
For the step up from Sol, see GPT-6.1 Sol vs GPT-6 Astra.
FAQ
Is GPT-6 Sol better than GPT-5.6 Sol?
For coding and terminal tasks, yes on Vals AI's tests. GPT-5.6 Sol still scores higher on several legal, tax, finance and competition-programming benchmarks.
How much cheaper is GPT-6 Sol?
Half the price: $2/$10 per million input/output tokens versus $4/$20 (up to 272K context).
When was GPT-6 Sol released?
September 22, 2026. GPT-5.6 Sol came out on July 9, 2026.
What is GPT-6.1 Sol?
The September 29, 2026 update to GPT-6 Sol, at the same $2/$10 price, positioned closer to the flagship GPT-6 Astra on coding and agents.
Do they have different context windows?
No. Both handle about 1.05 million input tokens.