Gemini 3.5 vs GPT-5.6
Pricing, benchmarks, and use case comparison
Verdict
Our pick: Gemini 3.5Pick Gemini 3.5 Flash for a fast, cheap, generally-available frontier model with a confirmed 1M context; pick the GPT-5.6 family if you have preview access and need the higher terminal-agent ceiling of its Sol, Terra, and Luna tiers.
Specs comparison
| Gemini 3.5 | GPT-5.6 | |
|---|---|---|
| Provider | Google DeepMind | OpenAI |
| Type | Closed source | Closed source |
| Context window | ✓1,048,576 tokens (Gemini 3.5 Flash; Pro variant not yet released) | Not announced |
| Input / 1M tokens | ✓$1.50 | 5 |
| Output / 1M tokens | $9.00 | 30 |
| Release date | 2026-05 | 2026-06 |
Benchmarks
| Benchmark | Gemini 3.5 | GPT-5.6 |
|---|---|---|
| Terminal-Bench 2.1 (coding) | 76.2% | - |
| MCP Atlas (tool use) | 83.6% | - |
| CharXiv Reasoning (multimodal) | 84.2% | - |
| Terminal-Bench 2.1 (Sol) | - | 88.8% |
| Terminal-Bench 2.1 (Terra) | - | 82.5% |
| Terminal-Bench 2.1 (Luna) | - | 84.3% |
| Terminal-Bench 2.1 | - | 88.8 |
| ExploitBench | - | Competitive with Anthropic Mythos Preview |
| ExploitGym | - | Significant improvements |
| GeneBench v1 | - | Not announced |
Scores sourced from official provider release posts and independent benchmark aggregators.
Capability and benchmarks
On terminal-agent tasks the GPT-5.6 family is ahead: Sol 88.8%, Luna 84.3%, Terra 82.5% on Terminal-Bench 2.1, versus Gemini 3.5 Flash's 76.2%. Gemini counters with published tool-use and multimodal strength: 83.6% MCP Atlas and 84.2% CharXiv chart reasoning. GPT-5.6 has the higher raw ceiling (coding 94, reasoning 94 vs Gemini 90/88), so if maximum intelligence is the goal, GPT-5.6 leads.
Availability, price, and context
Availability flips the verdict for most users. Gemini 3.5 Flash is generally available (default across the Gemini app, Search AI Mode, and the API) with a 1,048,576-token context and pricing of $1.50/$9 per 1M. GPT-5.6 is a gated limited preview with no published family-wide context window and per-tier pricing (Sol $5/$30, Terra $2.50/$15, Luna $1/$6). Gemini is far cheaper than Sol or Terra and ships today; only Luna approaches Gemini on price, and even then Gemini's context is confirmed.
Which to pick
- Pick Gemini 3.5 Flash for production today: fast output, low cost, a real 1M window, and strong multimodal and tool-use behavior.
- Pick the GPT-5.6 family if you have preview access and want to route across tiers for the highest terminal-agent scores, accepting gated access and unstated context.
Which should you choose?
Choose Gemini 3.5 if...
- →You need frontier agent/coding performance without frontier prices
- →Building autonomous agents that make many tool calls
- →High-throughput production workloads that were previously too costly on a Pro model
- →You want a strong default multimodal model with a 1M-token context window
Choose GPT-5.6 if...
- →You want to standardize on one model generation but route requests across cost/quality tiers
- →You are an approved preview partner exploring the newest OpenAI capabilities
- →Workloads spanning agentic coding, knowledge work, and research where tier flexibility helps