Gemini 2.5 Flash vs OpenAI o4-mini
Gemini 2.5 Flash is cheaper for every workload modelled here.
List prices checked
Specifications and rates
| Property | Gemini 2.5 Flash | OpenAI o4-mini |
|---|---|---|
| Input per 1M | $0.300 | $1.10 |
| Output per 1M | $2.50 | $4.40 |
| Cached input per 1M | $0.075 | $0.275 |
| Blended (3:1) | $0.850 | $1.93 |
| Context window | 1M | 200K |
| Max output | 66K | 100K |
| Inputs accepted | text, image, audio, video | text, image |
Source: Google pricing (May 2026) · OpenAI pricing (May 2026). Published list prices only — committed-use discounts, regional variation, and per-request charges are not included. Not yet independently re-checked against the vendor’s page.
Monthly cost by workload
Identical token volumes through both rate cards. Output-heavy profiles are where the ranking flips.
| Workload | Gemini 2.5 Flash | OpenAI o4-mini | Cheaper |
|---|---|---|---|
| In-app chat assistantA support or help assistant handling a few thousand conversations a month, with short prompts and short answers. | $19 | $44 | Gemini 2.5 Flashsaves $26/mo (58%) |
| RAG over documentsRetrieval-augmented answering where each request stuffs several retrieved passages into the prompt, so input dominates. | $128 | $396 | Gemini 2.5 Flashsaves $269/mo (68%) |
| Coding agentAn agentic loop that reads files and writes patches, generating heavy output and re-sending large context on every turn. | $370 | $880 | Gemini 2.5 Flashsaves $510/mo (58%) |
What each one is for
Gemini 2.5 Flash
by Google
The best price-to-context ratio on the market: a million tokens of multimodal input for a fraction of what frontier models charge, with optional thinking budgets.
OpenAI o4-mini
by OpenAI
Cheap reasoning, strong on maths and code relative to its price. Same caveat as every reasoning model: budget for the thinking tokens, not just the visible answer.
Common questions
- Is Gemini 2.5 Flash or OpenAI o4-mini cheaper in 2026?
- Gemini 2.5 Flash, for every workload modelled here. On a blended 3:1 basis it costs $0.850 per million tokens against OpenAI o4-mini's $1.93.
- Which has the larger context window?
- Gemini 2.5 Flash, at 1M tokens against 200K. A larger window only helps if you can afford to fill it — the cost of one full-context request is in the table above.
- Which is cheaper for output-heavy work like agents?
- Gemini 2.5 Flash, at $2.50 per million output tokens against $4.40. Reasoning tokens bill as output, so for agentic loops this axis usually decides the invoice regardless of what the input rates look like.
- What is not included in these figures?
- Batch-processing discounts, fine-tuning, long-context surcharges above a provider's standard tier, and any enterprise agreement. These are published pay-as-you-go list prices, checked against each provider's own pricing page on the date shown.
- Is switching from OpenAI o4-mini to Gemini 2.5 Flash worth it?
- On price alone it is about 56% cheaper on a blended basis. Whether that survives contact with your workload depends on output quality and on retry rate — a cheaper model that needs two attempts is not cheaper. Model the specific volumes in the calculator before you migrate.