🆕 GPT-6 Astra is now OpenAI's flagship. Launched 3 September 2026 at $10 input / $50 output per 1M tokens, Astra sits above the entire GPT-5.6 family and is rolling out to enterprises through the Trusted Access Program first. GPT-5.6 Sol remains fully supported and is roughly 2.5× cheaper. Full detail: GPT-6 Astra complete guide · Astra vs GPT-5.6 Sol head-to-head · Astra pricing and API costs.
GPT-5.6 is not a single model. It's a family of three — Sol, Terra and Luna — that OpenAI previewed on 26 June 2026 and made generally available on 9 July 2026 across ChatGPT, the API, Codex and GitHub Copilot. Instead of one frontier model plus a couple of "mini" spin-offs, OpenAI ships three models tuned to three jobs, plus finer controls over how hard the model thinks.
This page is the tier reference: what each model is for, what it actually costs today, what independent testing says, and how to choose. Vendor claims and independently-measured numbers are kept clearly apart. All pricing and specifications below were re-verified against OpenAI's developer documentation on 3 September 2026.
What are GPT-5.6 Sol, Terra and Luna?
They are three separate models released under one version number, split along the classic capability-versus-cost curve:
- Sol — the flagship of the 5.6 generation, built for frontier reasoning and long-horizon agentic work: complex coding across large codebases, multi-step agents, scientific reasoning and defensive security research. OpenAI's docs still describe it as its "flagship model for complex professional work", and the bare
gpt-5.6alias routes to it. - Terra — the balanced production workhorse. OpenAI positions it as matching GPT-5.5's performance at a fraction of the cost, aimed at high-volume business work: customer support, internal tools, document analysis, RAG.
- Luna — the cheapest and most latency-friendly tier, for summarization, drafting, classification and routine automation where price and speed beat reasoning depth.
The API names are gpt-5.6-sol, gpt-5.6-terra and gpt-5.6-luna. All three are reasoning models and all three carry identical context and output limits — the difference is capability and price, not window size.
What's the difference between Sol, Terra and Luna?
Here is the family at a glance, with the verified hard specifications alongside the positioning. Astra is included in the last row purely for scale.
| Model | Best for | Context window | Max output | Knowledge cutoff | Price in / out per 1M |
|---|---|---|---|---|---|
| GPT-5.6 Sol | Hard coding, long-horizon agents, security research, deep reasoning | 1,050,000 | 128,000 | 16 Feb 2026 | $4.00 / $20.00 |
| GPT-5.6 Terra | Support, internal tools, document analysis, everyday production | 1,050,000 | 128,000 | 16 Feb 2026 | $2.00 / $12.00 |
| GPT-5.6 Luna | Summarization, drafting, classification, high-volume automation | 1,050,000 | 128,000 | 16 Feb 2026 | $0.20 / $1.20 |
| GPT-6 Astra (for reference) | The hardest end-to-end work; OpenAI's current flagship | 1,050,000 | 128,000 | 30 Apr 2026 | $10.00 / $50.00 |
Two details worth knowing. Sol's usable input is capped at 922,000 tokens of the 1.05M window, with the remainder reserved for reasoning and output. And all three GPT-5.6 tiers support the full reasoning-effort ladder — none, low, medium, high, xhigh, max — defaulting to medium. Astra, notably, drops none: it always reasons.
How much does GPT-5.6 cost?
Current published API pricing per 1 million tokens, verified against OpenAI's pricing documentation on 3 September 2026. Batch requests run at exactly half the standard rate across every tier.
| Model | Input | Cached input | Output | Batch input | Batch output |
|---|---|---|---|---|---|
| Sol | $4.00 | $0.40 | $20.00 | $2.00 | $10.00 |
| Terra | $2.00 | $0.20 | $12.00 | $1.00 | $6.00 |
| Luna | $0.20 | $0.02 | $1.20 | $0.10 | $0.60 |
| GPT-6 Astra | $10.00 | $1.00 | $50.00 | $5.00 | $25.00 |
Sol's promotional pricing is still live — through at least 21 November 2026
This is the single most important cost fact on this page, and it is easy to get wrong because most write-ups still quote the launch price. On 21 August 2026 OpenAI cut Sol to $4 input / $20 output — 20% off input and 33% off output against the $5/$30 list price — and its documentation states the promotional pricing is "available at least through November 21, 2026."
That is a promotion with a floor, not a permanent list change, and it matters for two reasons. It makes Sol 2.5× cheaper than Astra on both input and output rather than 2×, which materially changes the step-up calculation below. And if you are building a 12-month cost model, budget against the $5/$30 list price for anything past November, not the promo.
Terra and Luna reached their current prices earlier, in OpenAI's 30 July 2026 cut — Luna down 80% (from $1/$6) and Terra down 20% (from $2.50/$15). Those were permanent list changes, not promotions.
Long-context and reasoning-token billing
Two billing rules catch teams out:
- Requests over 272,000 input tokens are surcharged on every tier: 2× the input and cached-input rate, 1.5× the output rate. So a long-context Sol call bills at $8 input / $0.80 cached / $30 output. The 1M-token window is real, but the last two-thirds of it costs double.
- Reasoning tokens are billed as output tokens. OpenAI's reasoning guide is explicit: they "are not visible via the API, they still occupy space in the model's context window and are billed as output tokens." At
xhighormaxeffort, invisible reasoning can dominate your bill. Pro mode behaves the same way — it "aggregates the model work performed to produce the final answer and bills those tokens at the selected model's standard token rates."
The practical consequence: comparing tiers on the headline output price alone is misleading, because higher-effort settings on Sol generate far more billable reasoning tokens than a medium-effort Terra call. Measure cost per completed task, not cost per token. For a worked comparison against a cheaper competitor, see our DeepSeek V4 vs GPT-5.6 cost breakdown.
Is GPT-5.6 still OpenAI's newest model?
No — not since 3 September 2026, when OpenAI released GPT-6 Astra, described in its changelog as "our most capable model, built for the hardest end-to-end work." Astra sits above the whole GPT-5.6 family for complex reasoning, coding, computer use, research and document creation.
What that does and does not change for GPT-5.6 users:
- Availability is staged. Astra is rolling out to enterprises through the Trusted Access Program first, with API and Plus/Pro/Business/Enterprise plan access described as coming soon. GPT-5.6 remains the generally-available option today.
- Astra is more constrained. It does not support
nonereasoning effort, does not accept customtemperature,top_por log probabilities. Function calling is listed as a supported feature and both Chat Completions and Responses are supported endpoints, though the hosted tools (web search, computer use, MCP and the rest) are documented for the Responses API. If your integration leans on those hosted tools or on sampling parameters, GPT-5.6 is the drop-in and Astra is a migration. - The price gap is wide. $10/$50 against Sol's promotional $4/$20 is 2.5× on both sides of the meter.
We keep Astra coverage deliberately brief here. The dedicated pages go deep: the complete GPT-6 Astra guide, Astra pricing and API costs, and the direct GPT-6 Astra vs GPT-5.6 Sol comparison.
Is GPT-5.6 being deprecated?
No. As of 3 September 2026, OpenAI's deprecations page lists no shutdown or retirement date for gpt-5.6-sol, gpt-5.6-terra or gpt-5.6-luna. The Astra launch did not come with a GPT-5.6 sunset notice.
The reverse is true, in fact: GPT-5.6 models appear on that page as the recommended replacements for older models that are retiring. gpt-5-2025-08-07 shuts down on 11 December 2026 with gpt-5.6-sol named as its successor, and gpt-5-mini-2025-08-07 retires the same day pointing at gpt-5.6-terra.
If you are on original GPT-5 or GPT-5-mini, 11 December 2026 is your real deadline — and the migration target is GPT-5.6, not Astra. Anyone already on GPT-5.6 has no forced move.
What are the max, Pro and Ultra modes?
These are not separate models or price tiers. They all run on gpt-5.6-sol and bill at Sol's standard rates — there is no gpt-5.6-sol-pro line item on OpenAI's pricing page.
maxreasoning effort — the top rung of the effort dial (none, low, medium, high, xhigh, max). More thinking time before answering, for problems where you would rather wait and be right. Remember the reasoning tokens are billed as output.- Sol Pro — spawns independent parallel agents that each work in isolation, then merges the best result. Successor to the old GPT-5.5-Pro approach. Billed by aggregating all the work at Sol's standard rates.
- Sol Ultra — goes further with four cooperating sub-agents that communicate mid-task and synthesize a joint answer. Burns several times the tokens of a standard Sol call; offered in Codex and ChatGPT Work. OpenAI reported it lifting Terminal-Bench 2.1 from Sol's 88.8% to 91.9%. Our Sol Ultra vs Claude Fable 5 piece digs into whether the extra compute pays.
Don't confuse Sol Ultra with Sol "Ultrafast." Ultrafast, announced 13 August 2026, is a service tier — the same Sol model served on Cerebras wafer-scale hardware — not a compute mode. Ultra is "same model, more thinking"; Ultrafast is "same model, served faster." It remains a limited preview with undisclosed pricing.
How good is GPT-5.6? (benchmarks)
Independent measurement
From Artificial Analysis (Intelligence Index v4.1.1, checked 3 September 2026, models run at maximum reasoning effort):
| Model | Intelligence Index | Rank | Output speed | Cost per task |
|---|---|---|---|---|
| GPT-5.6 Sol (max) | 61 | #10 / 202 | 76.5 tok/s | $0.95 |
| GPT-5.6 Terra (max) | 57 | — | 103 tok/s | — |
| GPT-6 Astra (max) | 61 | #8 / 202 | not yet measured | $1.67 |
Read that Astra row carefully, because it is the most interesting number on this page. On launch day, Astra and Sol both round to 61 on the same index — Astra ranks two places higher on the unrounded score, but it is not a generational leap on this particular aggregate, and it costs 76% more per completed task ($1.67 vs $0.95). Astra's headroom is likely in the harder end-to-end and computer-use work the index weights lightly, and its speed has not been measured yet. Treat this as a day-one reading that will move as the harness catches up, not a verdict.
Sol's cost per task has also fallen — from roughly $1.23 before the August promotion to $0.95 now — purely because of the price cut, not a model change.
Vendor-reported figures
These come from OpenAI's own GPT-5.6 launch materials and have not been independently reproduced. Useful for direction, not for settling arguments: SWE-Bench Pro around 64.6%, Agents' Last Exam around 52.7%, and Terminal-Bench 2.1 at 88.8% for standard Sol, rising to 91.9% in Ultra mode. On ARC-AGI — independently administered by the ARC Prize team — Sol posted 96.5% on ARC-AGI-1 and 92.5% on ARC-AGI-2.
OpenAI's system card rates all three tiers High capability but below the Critical threshold on cybersecurity and biology: in testing the models could find vulnerabilities and pieces of exploits but could not autonomously run end-to-end attacks against hardened targets. OpenAI's stated view is that GPT-5.6 is better at finding and fixing vulnerabilities than at exploiting them.
A tiering trap when you read competitors' charts
When Meta launched Muse Spark 1.2 in August 2026, its Terminal-Bench 2.1 comparison chart included GPT-5.6 Terra — the mid-tier model — but not Sol. Muse Spark's claimed 82.9% beats Terra's 81.8% by 1.1 points, but sits about six points below Sol's reported 88.8%. On price that substitution is defensible; as a flagship-versus-flagship read it is not, and several outlets reported it as one. Our Muse Spark 1.2 benchmark breakdown covers what is and isn't confirmed. The same care applies to any chart naming "GPT-5.6" without saying which tier — the gap between Luna and Sol is far larger than the gap between most competing flagships.
For a like-for-like flagship comparison, see Claude Opus 5 vs GPT-5.6.
How do you access GPT-5.6?
- ChatGPT — Plus, Pro, Business and Enterprise users can select Sol; Free and Go users get Terra.
- API — all three tiers are generally available, with the full reasoning-effort ladder and, for Sol, the Pro and Ultra modes.
- Codex and ChatGPT Work — including Sol Ultra for the hardest agentic coding.
- GitHub Copilot — Sol, Terra and Luna, all available since GA.
A fuller timeline of what shipped when is in our GPT-5.6 release date and what's new rundown.
Which GPT-5.6 tier should you pick?
Because the tiers map to jobs rather than to raw quality bands, routing is straightforward. Start here:
| If your task is… | Use | Why |
|---|---|---|
| Summaries, drafts, classification, high-volume automation | Luna | $0.20/$1.20 — 20× cheaper than Sol. "Good enough, instant, cheap" wins here. |
| Everyday production: support, internal tools, doc analysis, RAG | Terra | Index 57 at $2/$12 and the fastest of the three at ~103 tok/s. The volume workhorse. |
| Multi-step agents, hard refactors, security research, deep reasoning | Sol (with max, Pro or Ultra) | Index 61 at $0.95/task while the promo holds. Best value in the family right now. |
| Agentic work Sol measurably fails, or computer use / long end-to-end research | GPT-6 Astra | Only after Sol fails your evals — 76% more per task for no gain on the aggregate index. |
| Still on GPT-5 or GPT-5-mini | Sol or Terra | Those models shut down 11 Dec 2026; GPT-5.6 is the named replacement. |
The step-up rule, concretely. Move from Sol to Astra only when all three are true: (1) Sol at max effort measurably fails tasks you need to pass, on your own eval set, not on a public leaderboard; (2) the work is the long end-to-end reasoning, computer-use or research shape Astra was built for; and (3) you can absorb 2.5× the token price and a Responses-API migration. If any one of those is false, stay on Sol — it is the same measured intelligence at a lower cost per task today.
And a budget note that outlives this article: if you commit to Sol on the strength of $4/$20, model your spend past 21 November 2026 at the $5/$30 list price. The promotion is guaranteed only to that date.
What does the GPT-5.6 tiering mean for teams building agents?
With a 20× price spread between Luna and Sol inside one family, the right design is a routing one: send easy turns to Luna, the bulk to Terra, escalate only genuinely hard steps to Sol, and — if you adopt it — reserve Astra for the small slice that fails Sol. Teams that hard-code one expensive model for everything overpay by a large multiple, and that is now true within OpenAI's own lineup, not just across vendors.
Supervision matters more, not less. OpenAI's system card flags that GPT-5.6 shows a greater tendency than GPT-5.5 to go beyond the user's intent, including taking actions the user didn't ask for, even though absolute rates stay low. If you are wiring a model into tools, file systems or CI, scope agent permissions tightly, log every tool call, and keep a human gate on destructive actions.
A practical adoption checklist:
- Build an eval harness before you switch anything. It is the only thing that answers Sol-versus-Astra for your workload.
- Route by difficulty — Luna → Terra → Sol, with explicit escalation rules.
- Meter reasoning effort.
xhighandmaxbill invisible tokens as output; cap them. - Batch anything asynchronous. Half price across every tier, for work that can wait.
- Watch the 272K threshold. Crossing it doubles input cost — trim context before you pay the surcharge.
- Pin a known-good model version so you can revert instantly if behaviour drifts.
If you're new to wiring models into autonomous workflows, our AI coding agents complete guide covers the tool-use, sandboxing and supervision patterns this makes more relevant, not less.
The bottom line
GPT-5.6 is no longer OpenAI's newest family, but it is still the one most teams should be running. Nothing in it is deprecated, all three tiers are generally available today, and Sol's promotional pricing has made it better value since the Astra launch, not worse — same measured intelligence as Astra on the leading independent index, at a little over half the cost per task.
The decision rule is short. Default to Terra for production volume, drop to Luna where quality is not the constraint, reach for Sol on the hardest 10% of work, and evaluate Astra only when Sol demonstrably fails your own evals. Re-check the pricing page after 21 November 2026 — that is the one dated thing on this page that will change.
If you're building AI-powered products and want engineers who are fluent at directing, reviewing and containing agents rather than threatened by them, you can hire vetted remote developers through Codersera.
FAQ
What are GPT-5.6 Sol, Terra and Luna?
They are OpenAI's three GPT-5.6 model tiers, released together in July 2026. Sol is the flagship for hard coding, agents and deep reasoning. Terra is the balanced production model for support, internal tools and document work. Luna is the cheapest and fastest, built for summarization, classification and high-volume automation. All three share a 1.05M-token context window and a 128K max output.
Which GPT-5.6 tier should I use?
Default to Terra for production volume — it is the fastest of the three at roughly 103 tokens/sec and costs $2/$12 per 1M tokens. Drop to Luna where quality is not the binding constraint. Escalate to Sol for multi-step agents, hard refactors and security research. Route by difficulty rather than hard-coding one model, because the price spread across the family is about 20×.
How much does GPT-5.6 cost?
Per 1M tokens as of 3 September 2026: Sol is $4 input / $20 output (promotional), Terra $2/$12, Luna $0.20/$1.20. Cached input is $0.40, $0.20 and $0.02 respectively. Batch requests are exactly half price on every tier. Prompts above 272K input tokens are surcharged at 2× input and 1.5× output. Reasoning tokens bill as output tokens.
Is GPT-5.6 still OpenAI's newest model?
No. GPT-6 Astra launched on 3 September 2026 as OpenAI's most capable model, priced at $10 input / $50 output per 1M tokens, and is rolling out to enterprises via the Trusted Access Program before broader API and plan access. GPT-5.6 remains generally available and fully supported, and is the model most teams can still use today.
Is GPT-5.6 deprecated?
No. OpenAI's deprecations page lists no shutdown or retirement date for gpt-5.6-sol, gpt-5.6-terra or gpt-5.6-luna as of 3 September 2026, and the Astra launch carried no sunset notice. The opposite applies: GPT-5.6 models are the named replacements for older GPT-5 models. Original GPT-5 and GPT-5-mini shut down on 11 December 2026, migrating to Sol and Terra respectively.
Should I use GPT-5.6 Sol or GPT-6 Astra?
Start with Sol. On Artificial Analysis's Intelligence Index v4.1.1, both models round to 61, yet Astra costs $1.67 per task against Sol's $0.95 — 76% more for no gain on that aggregate. Move to Astra only when Sol at max effort measurably fails your own evals on long end-to-end reasoning or computer-use work, and you can absorb 2.5× the token price plus a Responses-API migration.
Is GPT-5.6 Sol's discounted price permanent?
No. The $4/$20 rate is promotional, introduced on 21 August 2026 as a 20% input and 33% output cut against the $5/$30 list price. OpenAI's documentation guarantees it only "at least through November 21, 2026." Terra and Luna's prices are different — those came from a permanent list-price cut on 30 July 2026 and carry no expiry.
What context window does GPT-5.6 have?
All three tiers have a 1,050,000-token context window with up to 128,000 output tokens. For Sol the usable input portion is capped at 922,000 tokens, with the rest reserved for reasoning and output. Be aware that any request exceeding 272,000 input tokens is billed at 2× the input rate and 1.5× the output rate on every tier.