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GPT-5.4 mini vs Gemini 3.5 Flash
A straight cost comparison of GPT-5.4 mini (OpenAI) and Gemini 3.5 Flash (Google Gemini), per 1,000,000 tokens, verified October 2026.
Rate-by-rate comparison
| Metric | GPT-5.4 mini | Gemini 3.5 Flash | Winner |
|---|---|---|---|
| Input / 1M | $0.75 | $1.50 | GPT-5.4 mini |
| Cached input / 1M | $0.075 | $0.15 | GPT-5.4 mini |
| Cache write / 1M | — | — | Tie |
| Output / 1M | $4.50 | $9 | GPT-5.4 mini |
| Context window | 400,000 | 1,000,000 | Gemini 3.5 Flash |
| Batch API | Yes | Yes | Tie |
| Long-context tier | None | None | — |
For per-token metrics, the lower number wins. For context window and batch support, the higher or broader option wins. A dash means the provider does not publish that rate: a missing cache-write fee means writes are not billed per token, while a missing cached-input rate means cache hits bill at the full input rate.
Blended cost: 1M input + 250K output
| Model | Blended cost | Difference |
|---|---|---|
| GPT-5.4 mini | $1.88 | Cheaper |
| Gemini 3.5 Flash | $3.75 | +$1.88 |
Ten workloads, two bills
The same two models, priced across ten workloads that differ only in their input:output ratio. Nothing else changes — no retries, no system prompt, no middleware.
| Workload | GPT-5.4 mini | Gemini 3.5 Flash | Winner |
|---|---|---|---|
| Classification 100K reqs · 500 in / 10 out | $42 | $84 | GPT-5.4 mini |
| Data extraction 10K reqs · 2K in / 200 out | $24 | $48 | GPT-5.4 mini |
| Support chat 1K reqs · 4K in / 600 out | $5.70 | $11.40 | GPT-5.4 mini |
| Code review 2K reqs · 8K in / 1.5K out | $25.50 | $51 | GPT-5.4 mini |
| Summarisation 1K reqs · 20K in / 1K out | $19.50 | $39 | GPT-5.4 mini |
| Agent loop 5K reqs · 12K in / 2K out | $90 | $180 | GPT-5.4 mini |
| Translation 500 reqs · 15K in / 15K out | $39.38 | $78.75 | GPT-5.4 mini |
| Long-document QA 200 reqs · 120K in / 800 out | $18.72 | $37.44 | GPT-5.4 mini |
| Cached RAG 1K reqs · 50K in (45K cached) / 1K out | $11.66 | $23.31 | GPT-5.4 mini |
| Nightly batch 10K reqs · 10K in / 2K out | $82.50 | $165 | GPT-5.4 mini |
GPT-5.4 mini wins 10 of 10, Gemini 3.5 Flash wins 0 of 10. The winner is set by the token mix, not by the headline rate.
Where the two bills cross over
GPT-5.4 mini is cheaper on both sides of the mix: $0.75 vs $1.50 per million input tokens, and $4.50 vs $9 per million output. No input:output ratio reverses that, so on price alone the other model never becomes the better choice — it has to win on context, latency or output quality.
Cost at four scales
The same support-chat workload (4K input, 600 output per request) at four monthly volumes.
| Requests / month | GPT-5.4 mini | Gemini 3.5 Flash | Difference |
|---|---|---|---|
| 100 | $0.57 | $1.14 | GPT-5.4 mini cheaper by $0.57 |
| 1,000 | $5.70 | $11.40 | GPT-5.4 mini cheaper by $5.70 |
| 10,000 | $57 | $114 | GPT-5.4 mini cheaper by $57 |
| 100,000 | $570 | $1,140 | GPT-5.4 mini cheaper by $570 |
What caching does to each bill
Caching only helps the part of the prompt that repeats. This is the support-chat workload (1,000 requests, 4,000 input tokens each) with an increasing share of that prompt served from a warm cache, written once on the first request.
| Cached share of the prompt | GPT-5.4 mini | Gemini 3.5 Flash | Winner |
|---|---|---|---|
| 0% | $5.70 | $11.40 | GPT-5.4 mini |
| 50% | $4.35 | $8.70 | GPT-5.4 mini |
| 80% | $3.54 | $7.08 | GPT-5.4 mini |
| 95% | $3.14 | $6.28 | GPT-5.4 mini |
Both models publish a cached-read rate, so the discount is comparable: GPT-5.4 mini reads cache at $0.075 per million, Gemini 3.5 Flash at $0.15.
Which one should you pick?
GPT-5.4 mini wins on classification, data extraction, support chat, code review, summarisation, agent loop, translation, long-document qa, cached rag, nightly batch, while Gemini 3.5 Flash wins on none of the ten workloads above.
Beyond price, the two differ on input rate ($0.75 vs $1.50); output rate ($4.50 vs $9); cached-input rate ($0.075 vs $0.15); context window (400,000 vs 1,000,000).
Batch mode is available on GPT-5.4 mini and Gemini 3.5 Flash, which halves the nightly job. Both publish cached-input discounts, so a stable system prompt is worth caching on either.
FAQ
Is GPT-5.4 mini cheaper than Gemini 3.5 Flash?
On a blended 1M-input-plus-250K-output workload, GPT-5.4 mini is cheaper by 50% ($1.88 vs $3.75). The gap changes for cache-heavy prompts and for batch jobs, as the workload table shows.
Which handles longer prompts, GPT-5.4 mini or Gemini 3.5 Flash?
GPT-5.4 mini has the larger context window (1,000,000 vs 400,000 tokens). Neither model publishes a long-context surcharge.
Do both models support prompt caching?
GPT-5.4 mini bills cached reads at $0.075 per 1M; Gemini 3.5 Flash at $0.15.
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