Gemini 2.5 Flash vs Gemini 1.5 Pro
Side-by-side comparison of Gemini 2.5 Flash (Google) and Gemini 1.5 Pro (Google). Exact API pricing per million tokens, context windows, output speed, and total cost on real-world prompts.
Specifications
| Spec | Gemini 2.5 Flash | Gemini 1.5 Pro |
|---|---|---|
| Provider | ||
| Model id | gemini-2.5-flash | gemini-1.5-pro |
| Input price (per 1M tokens) | $0.30 | $3.50 |
| Output price (per 1M tokens) | $2.50 | $10.50 |
| Context window | 1,048,576 | 2,000,000 |
| Output speed (tokens/sec) | ~200 | ~70 |
Cost on real prompts
Total cost = (input tokens × input price) + (output tokens × output price). Numbers below use the exact pricing tables published by each provider.
| Scenario | Input | Output | Gemini 2.5 Flash | Gemini 1.5 Pro | Cheaper |
|---|---|---|---|---|---|
| Short question + answer | 50 | 150 | $0.00039 | $0.001750 | Gemini 2.5 Flash |
| Code review on one file | 500 | 1,500 | $0.003900 | $0.017500 | Gemini 2.5 Flash |
| Long document summary | 5,000 | 500 | $0.002750 | $0.022750 | Gemini 2.5 Flash |
| Heavy reasoning task | 2,000 | 8,000 | $0.020600 | $0.091000 | Gemini 2.5 Flash |
| Full codebase analysis | 50,000 | 10,000 | $0.040000 | $0.280000 | Gemini 2.5 Flash |
Want the exact cost for your prompt instead of these examples? Open the cost calculator pre-loaded with both models →
When to pick which
Heuristics derived from the spec table above. Always validate on your own prompts before committing — these are starting points, not verdicts.
Pick Gemini 2.5 Flash for
- •output-heavy workloads (long-form generation, code, summaries) — gemini-2.5-flash is meaningfully cheaper per output token
- •input-heavy workloads (long context, RAG, document QA) — gemini-2.5-flash is cheaper per input token
- •latency-sensitive UX (chat, autocompletion) — gemini-2.5-flash streams faster (~200 vs ~70 tok/s)
Pick Gemini 1.5 Pro for
- •tasks needing a larger context window — gemini-1.5-pro fits 2x more tokens than gemini-2.5-flash
Switching between them
For most use cases, switching providers means updating the model id and the request shape if the providers differ. Within the same provider, it's usually a single-line change.
From Gemini 2.5 Flash to Gemini 1.5 Pro
# Before
model = "gemini-2.5-flash"
# After
model = "gemini-1.5-pro"If the providers differ (Google vs Google), you'll also need to swap the SDK / endpoint URL. Cross-provider migrations usually take 30 minutes to a few hours depending on how many features (streaming, function calling, tool use) you depend on.
Calculate cost on your own prompt
The examples above use generic input/output ratios. For an exact comparison, paste your real prompt into the calculator — it counts tokens with the right tokenizer for each model and shows side-by-side cost.
Open the calculator with both models →