Claude Opus 5 vs GPT-5.5 Pro

What are we comparing?

This comparison pits two frontier models, the ones you pick when quality comes first against each other: Claude Opus 5 and GPT-5.5 Pro, one from Anthropic, the other from OpenAI. The first dates from July 24, 2026, the second from April 23, 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.

What the benchmarks say

On our capability index, Claude Opus 5 scores 92.7 out of 100 and GPT-5.5 Pro 96.9. GPT-5.5 Pro leads by 4.2 points.

On the 3 benchmarks reported for both, Claude Opus 5 wins 0 times and GPT-5.5 Pro 2:

• GPQA Diamond (PhD-level science questions): Claude Opus 5 93.9%, GPT-5.5 Pro 93.9%
• OTIS Mock AIME (competition mathematics problems): Claude Opus 5 98.9%, GPT-5.5 Pro 100%
• FrontierMath (very hard research-level mathematics): Claude Opus 5 85.6%, GPT-5.5 Pro 87.7%

Budget

Claude Opus 5 costs $5 per million input tokens and $25 per million output tokens; GPT-5.5 Pro costs $30 and $180.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.15 with Claude Opus 5 versus $0.96 with GPT-5.5 Pro. Claude Opus 5 is 6.4 times cheaper, a gap that adds up quickly over 1,000 tasks: $810 difference.

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

Features and limits

GPT-5.5 Pro reads more in one go: 1,050,000 tokens of context (roughly 1,575 pages), versus 1,000,000 for Claude Opus 5.

Reasoning mode: Claude Opus 5 yes, GPT-5.5 Pro yes. Tool calling: Claude Opus 5 yes, GPT-5.5 Pro yes. Image input: Claude Opus 5 yes, GPT-5.5 Pro yes.

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

Knowledge cutoff: May 2026 for Claude Opus 5, December 1, 2025 for GPT-5.5 Pro.

In short

Our reading of the data:

• Choose Claude Opus 5 for a lower cost and a more recent release.
• Choose GPT-5.5 Pro for a higher capability index.

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