GPT-5.5 Pro versus Grok 4.6

The match-up at a glance

GPT-5.5 Pro and Grok 4.6 are the flagship models of two major developers, one from OpenAI, the other from xAI. GPT-5.5 Pro was released on April 23, 2026, Grok 4.6 on August 12, 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 Pro scores 96.9 out of 100 and Grok 4.6 86.1. GPT-5.5 Pro leads by 10.8 points.

On the 3 benchmarks reported for both, GPT-5.5 Pro wins 2 times and Grok 4.6 1:

• GPQA Diamond (PhD-level science questions): GPT-5.5 Pro 93.9%, Grok 4.6 94%
• OTIS Mock AIME (competition mathematics problems): GPT-5.5 Pro 100%, Grok 4.6 99.2%
• FrontierMath (very hard research-level mathematics): GPT-5.5 Pro 87.7%, Grok 4.6 66%

Pricing

GPT-5.5 Pro costs $30 per million input tokens and $180 per million output tokens; Grok 4.6 costs $2 and $6.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.96 with GPT-5.5 Pro versus $0.052 with Grok 4.6. Grok 4.6 is 18.5 times cheaper, a gap that adds up quickly over 1,000 tasks: $908 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 500,000 for Grok 4.6.

Reasoning mode: GPT-5.5 Pro yes, Grok 4.6 yes. Tool calling: GPT-5.5 Pro yes, Grok 4.6 yes. Image input: GPT-5.5 Pro yes, Grok 4.6 yes.

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

Knowledge cutoff: December 1, 2025 for GPT-5.5 Pro, February 1, 2026 for Grok 4.6.

In short

Our reading of the data:

• Choose GPT-5.5 Pro for a higher capability index and a larger context window.
• Choose Grok 4.6 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.