Grok 4.3 vs GPT-5.5: xAI vs OpenAI in 2026

GPT-5.5 is the stronger model on reasoning and complex tasks. Grok 4.3 is cheaper, faster, and has a dramatically larger context window. For most practical use cases, GPT-5.5 edges out on quality; for cost-sensitive or latency-sensitive applications, Grok 4.3 offers real advantages at a fraction of the API price.

Specs side by side

| | GPT-5.5 | Grok 4.3 | |---|---|---| | Lab | OpenAI | xAI | | Context window | 128K tokens | 1M tokens | | Input price | $5.00/M tokens | $1.25/M tokens | | Output price | $30.00/M tokens | $2.50/M tokens | | Speed | ~50-80 tok/s | ~207 tok/s | | SWE-bench Verified | 82.7% | Not published | | AI Analysis Index | 60.2 | 53 | | Consumer plan | ChatGPT Plus ($20/mo) | SuperGrok ($30/mo) |

The key differences

Price: Grok 4.3 costs 75% less on input and 92% less on output. At scale, this isn't a marginal difference — running one million output tokens through GPT-5.5 costs $30, through Grok 4.3 it costs $2.50.

Context window: Grok's 1M tokens vs GPT-5.5's 128K. For processing large codebases, long documents, or data-heavy tasks, Grok's context capacity is a real operational advantage.

Speed: 207 tokens per second vs GPT-5.5's 50-80. Grok is 2-4x faster. For real-time applications, voice interfaces, or interactive tools, this latency difference matters.

Reasoning quality: GPT-5.5 scores 60.2 on the Artificial Analysis Intelligence Index vs Grok 4.3 at 53. For complex multi-step reasoning, GPT-5.5 is the stronger model. Grok 4.3 improved a lot over its predecessor but hasn't closed the gap with the top OpenAI and Anthropic models.

Hallucination rate: Grok 4.3 holds the record at 78% non-hallucination on the Omniscience benchmark — above average for its tier. GPT-5.5 also performs well here, but Grok's always-on reasoning (which can't be disabled) may contribute to its factual accuracy.

Who should use Grok 4.3

Grok 4.3 is the right pick when:

You need to process very long documents or codebases (1M context)
Inference cost at scale is a significant constraint
Response speed is a product requirement (real-time chat, voice)
General tasks don't require frontier-level reasoning
You're already paying for X Premium+ and want model access bundled

Who should use GPT-5.5

GPT-5.5 is the right pick when:

You need top-tier reasoning on complex multi-step tasks
You rely on OpenAI's broader ecosystem (Sora, DALL-E, Assistants API)
Quality matters more than cost in your specific workflow
You're building on the ChatGPT platform with plugins or custom GPTs

On consumer pricing

This is the quirk: Grok 4.3 is cheaper at the API level but more expensive as a consumer subscription. SuperGrok costs $30/month; ChatGPT Plus costs $20/month. If you're using consumer products rather than the API, GPT-5.5 via ChatGPT Plus is better value per dollar.

The API economics flip this entirely — Grok's $1.25/$2.50 per million tokens versus GPT-5.5's $5.00/$30.00 makes Grok dramatically cheaper at any serious usage volume.