GPT-4 in ChatGPT has changed so much and so frequently. I've spent an inordinate time using both, side by side, and it has mostly failed to replicate the performance of their API offerings. While I don't have examples on hand right now, you can also look for yourself. Just look at the network requests in the web inspector. Here's the description of the Default ChatGPT GPT-4 model:

    {
      "slug": "gpt-4",
      "max_tokens": 4095,
      "title": "GPT-4",
      "description": "Our most capable model, great for tasks that require creativity and advanced reasoning.",
      "tags": [
        "gpt4"
      ],
      "capabilities": {},
      "product_features": {}
    }

Note the context size is 4095. Their model has been heavily optimized for speed and, presumably, cost.