GPT-5.5 vs GPT-6 Sol

What are we comparing?

GPT-5.5 and GPT-6 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 Sol on September 22, 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.

Performance

On our capability index, GPT-5.5 scores 89 out of 100 and GPT-6 Sol 89.2. The gap is too small to separate them.

On the 5 benchmarks reported for both, GPT-5.5 wins 1 time and GPT-6 Sol 3:

• GPQA Diamond (PhD-level science questions): GPT-5.5 94%, GPT-6 Sol 94.3%
• OTIS Mock AIME (competition mathematics problems): GPT-5.5 100%, GPT-6 Sol 100%
• FrontierMath (very hard research-level mathematics): GPT-5.5 85.3%, GPT-6 Sol 89.8%
• FrontierCode (advanced programming tasks): GPT-5.5 43%, GPT-6 Sol 49.3%
• APEX-Agents (professional tasks carried out by an agent): GPT-5.5 55.1%, GPT-6 Sol 54.3%

Budget

GPT-5.5 costs $5 per million input tokens and $30 per million output tokens; GPT-6 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 Sol. GPT-6 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.

Context and capabilities

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

Reasoning mode: GPT-5.5 yes, GPT-6 Sol yes. Tool calling: GPT-5.5 yes, GPT-6 Sol yes. Image input: GPT-5.5 yes, GPT-6 Sol yes.

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

Knowledge cutoff: December 1, 2025 for GPT-5.5, April 20, 2026 for GPT-6 Sol.

In short

Our reading of the data:

• Choose GPT-6 Sol for a lower cost and a more recent release.

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