GPT-5.1 vs GPT-5.5
Benchmarks, API pricing and specs, head to head. Data updated 2026-06-10.
GPT-5.1
59.6OpenAI · Nov 2025
A November 2025 update to GPT-5 with adaptive reasoning that spends thinking tokens only when a task needs them.
GPT-5.5
77.2OpenAI · Apr 2026
OpenAI's flagship reasoning model with a 1M-token context window, built for hard coding, science and long-horizon agentic work.
The verdict
GPT-5.5 wins 3 of the 3 benchmarks these models share, against 0 for GPT-5.1. On price the gap is dramatic: GPT-5.1 works out roughly 3.3x cheaper per blended million tokens. GPT-5.5 also takes 1M of context versus 400K for GPT-5.1.
Benchmark head-to-head 0–3
Specs & pricing
| GPT-5.1 | GPT-5.5 | |
|---|---|---|
| modhub Index | 59.6 | 77.2 |
| Input price / 1M | $1.25 | $5 |
| Output price / 1M | $10 | $30 |
| Context window | 400K | 1M |
| Max output | 128K | 128K |
| Open weights | no | no |
| Reasoning model | yes | yes |
| Multimodal input | text, image | text, image |
| Knowledge cutoff | Sep 2024 | Jan 2026 |
| Released | Nov 2025 | Apr 2026 |
| Example monthly cost* | $27.50 | $95.00 |
* 10M input + 1.5M output tokens per month at list prices, no caching. Green = better value on that row.
Frequently asked questions
- Which is better, GPT-5.1 or GPT-5.5?
- GPT-5.5 wins 3 of the 3 benchmarks these models share, against 0 for GPT-5.1. On price the gap is dramatic: GPT-5.1 works out roughly 3.3x cheaper per blended million tokens. GPT-5.5 also takes 1M of context versus 400K for GPT-5.1.
- Which is cheaper, GPT-5.1 or GPT-5.5?
- GPT-5.1 costs $1.25/$10 per million input/output tokens, while GPT-5.5 costs $5/$30. For a typical workload of 10M input and 1.5M output tokens per month, that's $27.50 versus $95.00.
- Which model is better for coding, GPT-5.1 or GPT-5.5?
- On SWE-bench Verified — the standard agentic-coding benchmark — GPT-5.5 scores 82.6% versus 76.3% for GPT-5.1, making GPT-5.5 the stronger pick for coding agents.