GPT-5.6 Terra vs Gemini 3.5 Flash
OpenAI's GPT-5.6 Terra and Google's Gemini 3.5 Flash both target production language workloads, but they price and behave differently. Here is the side-by-side.
Pricing checked against provider documentation on . How we verify
The short answer
Gemini 3.5 Flash is the cheaper option — roughly 1.3x less on a blended workload, and it suits agentic loops and sub-agent fleets. GPT-5.6 Terra justifies its premium when you need balanced production workloads.
OpenAI • GPT-5.6
$2.00 / $12.00
/ 1M tokens (input / output)
The everyday tier of the GPT-5.6 family, roughly corresponding to the old 'mini' slot but benchmarking above the previous generation's flagship. For most application backends this is the default worth trying before reaching for Sol, since it clears Claude Fable 5 on several evals at a fraction of the cost.
Google • Gemini 3.5
$1.50 / $9.00
/ 1M tokens (input / output)
Google's most capable Flash model, tuned for the agentic era: sub-agent deployment, multi-step workflows, and rapid coding iterations at scale. Supports search grounding, function calling, structured outputs, and computer use in preview. Note that it is pricier than the Gemini 3 Flash preview it replaced.
Input price
Gemini 3.5 Flash is 25% cheaper than GPT-5.6 Terra on input tokens.
Output price
Gemini 3.5 Flash is 25% cheaper than GPT-5.6 Terra on output tokens — usually the side that dominates the bill.
Monthly cost at three workload sizes
Standard (non-batch, non-cached) rates. Reasoning models will exceed these figures because thinking tokens bill as output.
| Workload | GPT-5.6 Terra | Gemini 3.5 Flash | Difference |
|---|---|---|---|
| Light — 1M in / 200K out | $4 | $3 | $1 |
| Moderate — 10M in / 2M out | $44 | $33 | $11 |
| Heavy — 100M in / 20M out | $440 | $330 | $110 |
Specification comparison
| Attribute | GPT-5.6 Terra | Gemini 3.5 Flash |
|---|---|---|
| Input (/ 1M tokens) | $2.00 | $1.50 |
| Output (/ 1M tokens) | $12.00 | $9.00 |
| Cached input | $0.20 | — |
| Context window | 1,048,576 tokens | 1,048,576 tokens |
| Max output | 128,000 tokens | 65,536 tokens |
| Native reasoning | Yes | Yes |
| Knowledge cutoff | 2026-02 | 2025-01 |
| Relative latency | medium | low |
| Open weights | No | No |
| API model ID | gpt-5.6-terra | gemini-3.5-flash |
| Status | stable | stable |
GPT-5.6 Terra: Cut 20% from the $2.50/$15 launch price on 2026-07-30.
Gemini 3.5 Flash: Flat rate at any context length, unlike Gemini 3.1 Pro's 200K cliff.
Choose GPT-5.6 Terra if…
- Customer support and chat backends
- RAG and document processing pipelines
- Mid-complexity coding tasks
- Tool-calling agents at scale
Choose Gemini 3.5 Flash if…
- Sub-agent fleets and orchestration
- Fast coding iteration loops
- Search-grounded answers
- Multimodal ingestion at scale
Frequently asked
Is GPT-5.6 Terra or Gemini 3.5 Flash cheaper?
Gemini 3.5 Flash is cheaper. On a blended 3:1 input-to-output workload it costs about 1.3x less than GPT-5.6 Terra.
Which has the larger context window, GPT-5.6 Terra or Gemini 3.5 Flash?
Both accept up to 1.05M tokens, so context is not a differentiator here.
Should I use GPT-5.6 Terra or Gemini 3.5 Flash?
Pick GPT-5.6 Terra for balanced production workloads. Pick Gemini 3.5 Flash for agentic loops and sub-agent fleets. If cost dominates the decision, Gemini 3.5 Flash wins; if you need the capability ceiling, benchmark both on your own evals before committing.