What is GPT-5.6 'Sol'?
OpenAI announced GPT-5.6, codenamed Sol, on June 26, 2026 — the follow-up to GPT-5.5. It launched as a limited preview for a small group of trusted partners, with general availability across ChatGPT, Codex, and the API planned in the following weeks. The family includes three variants: Sol, Terra, and Luna.
What's known vs rumored
OpenAI's own preview confirms the staged rollout and the three-variant lineup. Beyond that, reporting points to a much larger context window (up to ~1.5M tokens vs 400K on GPT-5.5), stronger long-horizon agent reliability across 100+ tool calls, and dynamic effort control. Treat the unconfirmed specs as expectations, not promises, until the API docs land.
GPT-5.6 API access — when can you use it?
As of now the API is not broadly open; it started with a limited partner preview. Historically OpenAI opens the API within days to a few weeks of the ChatGPT rollout, and GPT-5.6 is expected to be a drop-in replacement for GPT-5.5 — same wire format, swap the model id.
What to ship today
Migrating vendors now and back later costs more than waiting. The pragmatic move: keep building on the OpenAI wire format with GPT-5.5, or route hard tasks to Claude Opus 4.8 / Sonnet 5 — all available on KissAPI today at up to 80% off list price, behind one OpenAI-compatible endpoint. When GPT-5.6 opens up, switching is a one-line model-id change.
curl https://api.kissapi.ai/v1/chat/completions \
-H "Authorization: Bearer $KISSAPI_KEY" \
-H "Content-Type: application/json" \
-d '{"model":"claude-opus-4-8","messages":[{"role":"user","content":"hi"}]}'Ship now, upgrade later
Build on GPT-5.5 and Claude today at up to 80% off. One key, one endpoint. $1 free to start.
Start Free — $1 creditFAQ
When was GPT-5.6 released?
OpenAI announced GPT-5.6 'Sol' on June 26, 2026, starting with a limited preview for trusted partners. Broader ChatGPT, Codex, and API availability was planned for the following weeks.
Can I access the GPT-5.6 API now?
Broad API access wasn't available at announcement — it began as a limited partner preview. OpenAI typically opens the API within days to weeks of the ChatGPT rollout.
What are Sol, Terra, and Luna?
They're the three variants of the GPT-5.6 family that OpenAI previewed together, with Sol as the headline model.
What should I use until GPT-5.6 opens up?
GPT-5.5 or Claude Opus 4.8 / Sonnet 5. All are available on KissAPI today at up to 80% off, and GPT-5.6 is expected to be a drop-in replacement, so switching later is a one-line change.