You can get very close results to GPT 5.5 by using GPT 5.4 with a highly detailed prompt.

I ran a small test to check this properly. I generated the same technical content into summaries using both GPT 5.4 and GPT 5.5, across four different prompt detail levels (Low to XHigh). Then I asked ChatGPT to rank all 8 outputs blindly, without giving it any scoring categories or guidelines — so my own preferences wouldn’t influence the result.

Here’s how it turned out:

Rankings (1 = best):

1. GPT 5.5 XHigh — 9.4/10
   Best overall balance of technical depth, accuracy, and framing.

2. GPT 5.4 XHigh — 9.0/10
   Extremely close to the top. Clean, well-structured, and strong.

3. GPT 5.4 High — 8.7/10
   Solid and grounded, with good references to the source material.

4. GPT 5.5 Medium — 8.5/10

5. GPT 5.5 High — 8.5/10
   Both clear and reliable.

6. GPT 5.5 Low — 8.3/10
   Held up surprisingly well for a lighter prompt.

7. GPT 5.4 Medium — 8.0/10

8. GPT 5.4 Low — 7.6/10

Main takeaway:
Once you go all-in on prompt detail (XHigh), the performance gap between 5.4 and 5.5 becomes quite small. This gives you a practical, lower-cost option without losing much quality.