GPT 5.6 Sol is the flagship model in OpenAI's GPT-5.6 family, the first generation to ship as three named tiers: Sol for frontier reasoning, Terra for balanced everyday work, and Luna for high-volume, low-latency tasks. OpenAI announced the family on June 26, 2026 as a limited preview and moved it to general availability in July 2026 — so if you searched for the gpt 5.6 sol api release date, the answer is: it is live now, and you can call it on GPTProto today.
Sol targets the work where correctness matters more than cost: long-horizon agentic coding, scientific reasoning, and structured data synthesis. It introduces two capabilities absent from GPT-5.5 — Programmatic Tool Calling, which lets the model write and execute JavaScript in an isolated V8 runtime with no network access, and an ultra multi-agent mode that coordinates four agents in parallel, lifting Terminal-Bench 2.1 from 88.8% to 91.9%.
| Spec | gpt-5.6-sol |
|---|---|
| Provider | OpenAI |
| Modality | Text in / text out |
| Context window | 1,050,000 tokens |
| Max output | 128,000 tokens |
| Reasoning levels | Medium / High / Extra High / max |
| Structured outputs | Strict JSON schema mode |
| Tool use | Programmatic Tool Calling (isolated JS runtime) |
| Prompt caching | Reads at 90% discount; writes billed 1.25x input rate |
| GPTProto price | $4 input / $24 output per 1M tokens |
| Official price | $5 input / $30 output per 1M tokens |
| Model string | gpt-5.6-sol |
The openai gpt 5.6 sol api token pricing above is flat on GPTProto. Every token is billed from the same balance you use for Claude, Gemini, DeepSeek, and 200+ other models.
The GPT 5.6 Family: Sol vs Terra vs Luna
The gpt-5.6 alias in OpenAI's API routes to Sol — so if you are integrating "GPT 5.6" without a tier suffix, this is the model you get. Within the gpt 5.6 family, the tiers trade capability for cost:
| Tier | Best for | AA Coding Agent Index | Official / 1M | On GPTProto |
|---|---|---|---|---|
| gpt-5.6-sol (this page) | Frontier reasoning, long agent runs | 80 | $5 / $30 | $4 / $24 |
| gpt-5.6-terra | Everyday production traffic | 77 | $2.50 / $15 | $2 / $12 |
| gpt-5.6-luna | High-volume, latency-sensitive | 74.6 | $1 / $6 | $0.80 / $4.80 |
Rule of thumb: prototype on Sol to establish a quality ceiling, then test whether Terra holds it at half the price. All three tiers share one API key and one balance on GPTProto.
GPT 5.6 Sol vs GPT 5.5
Both models sit on the same official rate card ($5/$30 per 1M) and the same GPTProto rate ($4/$24), which makes this an unusual upgrade: the capability jump costs nothing extra. The gpt 5.6 sol api cost only changes with how many tokens your workload burns — and OpenAI reports Sol uses up to 54% fewer output tokens on agentic coding than the next-highest-scoring model, so per-task cost can actually fall.
| gpt-5.6-sol | gpt-5.5 | |
|---|---|---|
| Terminal-Bench 2.1 (agentic coding) | 88.8% (91.9% with ultra) | 88.0% |
| Artificial Analysis Coding Agent Index | 80 (Codex harness) | 76 (Codex harness) |
| Artificial Analysis Intelligence Index | 59 (max reasoning) | 55 |
| ExploitBench2 (vulnerability-to-execution) | 73.5% | 47.9% |
| Reasoning modes | Medium → max, plus ultra multi-agent | Standard effort levels |
| Programmatic Tool Calling | Yes (isolated JS runtime) | No |
| Official price per 1M | $5 / $30 | $5 / $30 |
| GPTProto price per 1M | $4 / $24 | $4 / $24 |
Honest read: if your workload is short chat completions, GPT-5.5 remains fine and slightly faster to first token in some setups. Choose gpt 5.6 sol vs gpt 5.5 in favor of Sol when tasks run long — multi-file coding, agent loops that previously stalled mid-run, or anything needing strict structured output at scale. Both model strings work on GPTProto at the same $4/$24 rate, so an A/B test is a one-line change. See the gpt-5.5 page for its full spec sheet.
Switching from the OpenAI API
The gpt-5.6-sol api on GPTProto is OpenAI-compatible. Migration is two edits: point base_url at GPTProto and swap in your GPTProto key. The model string gpt-5.6-sol stays identical, so existing prompts, schemas, and tool definitions carry over unchanged.
Three reasons teams route this model through an aggregator instead of going direct:
- Price. $4/$24 versus $5/$30 per 1M tokens — a 20% off gpt 5.6 sol api rate that compounds fast on reasoning-heavy workloads, where output tokens dominate the bill.
- No separate account friction. OpenAI requires Advanced Account Security with hardware-backed passkeys by September 1, 2026 to retain access to its most cyber-capable frontier models. On GPTProto, one API key covers gpt-5.6-sol and every other model on the platform — no extra security enrollment, no region-based sign-up hurdles.
- One balance, 200+ models. Benchmark gpt-5.6-sol against Claude, Gemini, or DeepSeek from the same dashboard without maintaining four provider accounts.
If you need a rollback path, keep gpt-5.5 as a fallback string in your config — same endpoint, same key.
