GPT-5.5 Pro vs OpenAI gpt-oss-120b
Compare GPT-5.5 Pro and OpenAI gpt-oss-120b on the metrics that decide an agent workload.
| Metric | GPT-5.5 Pro | OpenAI gpt-oss-120b |
|---|---|---|
| Provider | OpenAI | Fireworks AI |
| Input / 1M | $30.00 | $0.15 |
| Output / 1M | $180.00 | $0.60 |
| Cache read / 1M | $30.00 (−0%) | $0.01 (−90%) |
| Reuse-adj @55% | $67.50 | $0.21 |
| Context | 1.1M | 131K |
| Cache capture | 90% | 79% |
| Warm TTFT | 900ms (−53%) | 120ms (−64%) |
| Quality index | 97 | 79 |
Teal marks the better value in each row. Reuse-adjusted assumes 55% prefix reuse and a 25% output share.
Pick GPT-5.5 Pro when it scores higher on the composite quality index, it carries the larger 1.1M context window, it captures more of the available reuse.
Pick OpenAI gpt-oss-120b when it is cheaper once prefix reuse is priced in, it answers faster on warm cache hits, it is open-weights for on-prem and regulated lanes.
GPT-5.5 Pro leads on quality while OpenAI gpt-oss-120b leads on reuse-adjusted cost. Send latency- and budget-sensitive volume to OpenAI gpt-oss-120b and reserve GPT-5.5 Pro for the hard requests. Zumik's aliases route between them automatically under policy.
GPT-5.5 Pro vs OpenAI gpt-oss-120b, answered.
Is GPT-5.5 Pro or OpenAI gpt-oss-120b cheaper?
At 55% prefix reuse, GPT-5.5 Pro blends to about $67.50 per 1M tokens and OpenAI gpt-oss-120b to about $0.21. OpenAI gpt-oss-120b is cheaper on that basis.
Which has the larger context window?
GPT-5.5 Pro has the larger window: 1.1M vs 131K tokens.
Which captures more reuse?
GPT-5.5 Pro shows higher measured cache capture (90% vs 79%) in the Zumik corpus.
Let an alias pick for you.
Route to whichever model wins under current policy automatically. Zumik resolves the alias to the best fit per request, so you never hard-code a loser.