Gemini 3.5 Flash vs GPT-5.5 Pro
Compare Gemini 3.5 Flash and GPT-5.5 Pro on the metrics that decide an agent workload.
| Metric | Gemini 3.5 Flash | GPT-5.5 Pro |
|---|---|---|
| Provider | Google Gemini | OpenAI |
| Input / 1M | $1.50 | $30.00 |
| Output / 1M | $9.00 | $180.00 |
| Cache read / 1M | $0.15 (−90%) | $30.00 (−0%) |
| Reuse-adj @55% | $2.82 | $67.50 |
| Context | 1M | 1.1M |
| Cache capture | 81% | 90% |
| Warm TTFT | 150ms (−61%) | 900ms (−53%) |
| Quality index | 86 | 97 |
Teal marks the better value in each row. Reuse-adjusted assumes 55% prefix reuse and a 25% output share.
Pick Gemini 3.5 Flash when it is cheaper once prefix reuse is priced in, it answers faster on warm cache hits.
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.
GPT-5.5 Pro leads on quality while Gemini 3.5 Flash leads on reuse-adjusted cost. Send latency- and budget-sensitive volume to Gemini 3.5 Flash and reserve GPT-5.5 Pro for the hard requests. Zumik's aliases route between them automatically under policy.
Gemini 3.5 Flash vs GPT-5.5 Pro, answered.
Is Gemini 3.5 Flash or GPT-5.5 Pro cheaper?
At 55% prefix reuse, Gemini 3.5 Flash blends to about $2.82 per 1M tokens and GPT-5.5 Pro to about $67.50. Gemini 3.5 Flash is cheaper on that basis.
Which has the larger context window?
GPT-5.5 Pro has the larger window: 1.1M vs 1M tokens.
Which captures more reuse?
GPT-5.5 Pro shows higher measured cache capture (90% vs 81%) 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.