GPT-5.5 versus GPT-6.1 Sol

What are we comparing?

GPT-5.5 and GPT-6.1 Sol are two frontier models, the ones you pick when quality comes first, both built by OpenAI. GPT-5.5 was released on April 23, 2026, GPT-6.1 Sol on September 29, 2026.

All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.

Which one is more capable?

On our capability index, GPT-5.5 scores 89 out of 100 and GPT-6.1 Sol 92.1. GPT-6.1 Sol leads by 3.1 points.

On the 5 benchmarks reported for both, GPT-5.5 wins 0 times and GPT-6.1 Sol 4:

• GPQA Diamond (PhD-level science questions): GPT-5.5 94%, GPT-6.1 Sol 95.4%
• OTIS Mock AIME (competition mathematics problems): GPT-5.5 100%, GPT-6.1 Sol 100%
• FrontierMath (very hard research-level mathematics): GPT-5.5 85.3%, GPT-6.1 Sol 93.7%
• FrontierCode (advanced programming tasks): GPT-5.5 43%, GPT-6.1 Sol 50.2%
• APEX-Agents (professional tasks carried out by an agent): GPT-5.5 55.1%, GPT-6.1 Sol 60%

Pricing

GPT-5.5 costs $5 per million input tokens and $30 per million output tokens; GPT-6.1 Sol costs $2 and $10.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.16 with GPT-5.5 versus $0.06 with GPT-6.1 Sol. GPT-6.1 Sol is 2.7 times cheaper, a gap that adds up quickly over 1,000 tasks: $100 difference.

Run the numbers with your own volumes in the agent cost calculator.

Under the hood

Both models have the same context window: 1,050,000 tokens, roughly 1,575 pages.

Reasoning mode: GPT-5.5 yes, GPT-6.1 Sol yes. Tool calling: GPT-5.5 yes, GPT-6.1 Sol yes. Image input: GPT-5.5 yes, GPT-6.1 Sol yes.

Neither publishes its weights: both are used through an API.

Knowledge cutoff: December 1, 2025 for GPT-5.5, April 30, 2026 for GPT-6.1 Sol.

In short

Our reading of the data:

• Choose GPT-6.1 Sol for a higher capability index, a lower cost and a more recent release.

This verdict relies on public figures; it does not replace a trial on your own tasks.