GPT-6 Sol and Luna Launch: $5 Pricing, 1.05M Context

Published September 23, 2026 - San Francisco, California. OpenAI launched GPT-6 Sol and GPT-6 Luna on September 22, 2026 at $5 and $1 per million input tokens - half the cost of the GPT-5.6 Sol and Luna pair they replace.

Both models share a 1.05 million token context window. Sol is the flagship coding, research, and security model; Luna is the high-volume everyday tier that is becoming the default for ChatGPT Free and Go users this week (OpenAI, September 22, 2026).

At a glance

• Released September 22, 2026; API IDs `gpt-6-sol` and `gpt-6-luna`.
• GPT-6 Sol: $5 input / $30 output per million tokens; cache reads $0.20 per million.
• GPT-6 Luna: $1 input / $6 output per million tokens; cache reads $0.01 per million.
• 50% cheaper than GPT-5.6 Sol/Luna at input and output.
• 1.05M context, 922K input max, 128K output max - unchanged from GPT-6 Astra.
• Sol rolled out in ChatGPT Work, Codex, and API on September 22; Luna becomes Free/Go default this week.
• New thought slider for Plus/Pro on Sol; Think button for harder questions on Luna.
• GPT-6 Astra (September 3, 2026) remains OpenAI's premium reasoning model.

Data last verified September 23, 2026 from OpenAI's announcement and API pricing pages, the model catalog, TechCrunch, and Mashable.

Quick Answer

OpenAI released GPT-6 Sol and GPT-6 Luna on September 22, 2026 at $5 and $1 per million input tokens - cutting prices by 50% versus the GPT-5.6 series.

Both models keep the 1.05 million token context window. Sol is the new flagship for coding, research, and security work; Luna is positioned for high-volume everyday tasks and is rolling out as the default for Free and Go ChatGPT users this week (OpenAI, September 22, 2026).

Sol and Luna sit one tier below GPT-6 Astra in OpenAI's lineup.

Astra, released September 3, 2026, remains the premium reasoning model with the strongest published benchmarks (OpenAI model catalog, September 2026).

What changed from GPT-5.6 Sol and GPT-5.6 Luna

The GPT-6 series is the second cut at the GPT-6 architecture OpenAI introduced on June 26, 2026 with GPT-5.6 Sol, Terra, and Luna. GPT-6 Astra followed on September 3, 2026; Sol and Luna on September 22 close the family.

Three moves stand out against GPT-5.6.

First, list pricing is cut in half on both input and output for Sol and Luna.

Second, cached input costs on Sol drop to $0.20 per million from GPT-5.6 Sol's $0.50 - an effective 60% cut for workflows that benefit from prompt caching.

Third, OpenAI claims GPT-6 Sol makes about half as many factual errors as GPT-5.6 Sol on internal evaluation (OpenAI, September 22, 2026).

Context is unchanged: 1.05 million tokens, 922K input max, 128K output max. Latency has not been disclosed; pricing pages list GPT-6 Sol's long-context tier as 1M tokens at the same rate as the under-200K tier (OpenAI API pricing, September 22, 2026).

Pricing for GPT-6 Sol and GPT-6 Luna

Direct API rates in US dollars per million tokens, verified against the OpenAI pricing page on September 22, 2026:

Sol is the same price tier as Astra but with cheaper caching; Luna is the cheapest OpenAI model currently sold on the API. GPT-5.5 Pro remains the maximum-effort premium tier (OpenAI API pricing, September 22, 2026).

How Sol and Luna were trained

OpenAI has not published training-compute or architecture details for GPT-6 Sol or Luna. The introduction post says Sol and Luna were trained with the same methods as GPT-6 Astra, distributing Astra's frontier capability into faster and cheaper form factors.

That distribution story carries the cost claim: OpenAI attributes the 50% price cut to improvements in caching and inference rather than to a lossier model. The internal factuality claim - 'about half as many mistakes as GPT-5.6 Sol' - lines up with the Astra benchmark position (OpenAI, September 22, 2026).

Day-one rollout and access

The September 22, 2026 launch followed a tier-by-tier rollout:

• GPT-6 Sol: ChatGPT Work, Codex, and the API on launch day for Plus, Pro, Business, and Enterprise; Sol Pro to Pro and Enterprise only.
• GPT-6 Luna: rolling out throughout the week to Free and Go users with unlimited text chats and a new Think button for harder questions; rate limits remain on file uploads, image generation, and other tools.
• Work and Codex: the version of GPT-6 Sol that powers Work and Codex is unchanged from the prior release.

The new thought slider on ChatGPT Sol lets users pick the reasoning effort per message. The settings run from none through low, medium, high, xhigh, and a new max effort for the deepest reasoning - the same effort taxonomy as GPT-6 Astra (OpenAI, September 22, 2026).

How GPT-6 Sol compares to the frontier

OpenAI published three benchmark numbers for GPT-6 Sol in the launch post. On FrontierCode 1.1 Main - a 'mergeability' grading rubric for agent-written code changes - GPT-6 Sol improves substantially over GPT-5.6 Sol and matches Claude Fable 5.1 xhigh at much lower cost.

On DeepSWE v1.1, GPT-6 Sol max effort scores 68.8% on complex software-engineering tasks in real codebases, within 1.1 percentage points of Claude Fable 5's best published score of 69.9% at xhigh effort - at roughly 80% lower cost per task.

On Terminal-Bench 2.1, GPT-6 Sol sets a new state of the art for command-line workflows. OpenAI notes these are agentic-coding benchmarks rather than chat benchmarks; for general knowledge work, GPT-6 Astra remains the higher-scoring OpenAI model (OpenAI, September 22, 2026).

How GPT-6 Luna compares to GPT-5.6 Luna

GPT-6 Luna replaces GPT-5.6 Luna in the everyday tier. OpenAI positions Luna for 'easy, lower-stakes everyday tasks' - the same workload slot GPT-5.6 Luna filled - and says the new model outperforms GPT-5.6 Luna at one-fourth the API price.

Luna's pricing makes it OpenAI's cheapest API model currently sold. The cache price of $0.01 per million tokens is roughly one cent per million - cheap enough that cached-prompt workflows can run at near-zero input cost (OpenAI, September 22, 2026).

What to do today

Three workflows are worth a same-day test. First, swap GPT-5.6 Sol for GPT-6 Sol on coding-agent pipelines. At the same input price as GPT-5.6 was a year ago and roughly half of GPT-5.6, the cost-performance math has changed since the May pricing reset.

Second, route Free-tier or high-volume Q&A traffic to GPT-6 Luna once it becomes your default. The $0.01 per million cache price makes cached-heavy RAG workflows viable at scale.

Third, audit factual-error behaviour on long-context recall tasks before retraining evaluation suites. OpenAI's internal factuality claim is bold; external evaluators typically take weeks to publish corroborating results.

GPT-6 Sol API changes are live in the OpenAI dashboard today. Luna's API tier is already published; the Free/Go default swap completes inside the launch week (OpenAI, September 22, 2026).

What was not announced

Three things stayed off the launch post. There is no GPT-6 Terra - the openai.com catalog lists gpt-6-astra, gpt-6-sol, gpt-6-luna only; GPT-5.6 Terra remains a separate generation. There is no separate 'reasoning' SKU for GPT-6 Sol; users pick effort via the slider.

There is no public training-compute number for either model. OpenAI has not disclosed token-count, GPU-hours, or dataset size for the GPT-6 series; third-party model-card publications remain the only public data on training scale (OpenAI model catalog, September 22, 2026).

Frequently Asked Questions

Reviewers summarised the most common September 23 reader questions - the same questions above plus their follow-ups.

Is GPT-6 Sol better than GPT-6 Luna for coding?

Yes, on published benchmarks. GPT-6 Sol leads on Terminal-Bench 2.1, FrontierCode, and DeepSWE; GPT-6 Luna is positioned for high-volume, lower-difficulty work where cost dominates capability. For agentic coding or multi-step refactor tasks, route to Sol.

For quick code-completion or one-shot utilities, Luna is the cost-effective choice (OpenAI, September 22, 2026; TechCrunch, September 22, 2026).

Does GPT-6 Sol replace GPT-6 Astra?

No. Astra remains the premium reasoning tier with the highest published benchmark scores on GPT-6.

Sol is positioned for cost-effective everyday agentic coding where pricing matters more than peak accuracy. Customers should run a small benchmark suite against their own workload to decide when to use which model (OpenAI, September 22, 2026).

When does GPT-6 Luna become the default for Free and Go users?

OpenAI said GPT-6 Luna 'will become the default model for Free and Go users this week' - inside the September 22 to 28 launch week.

Existing ChatGPT Free and Go accounts get Luna with unlimited text chats on rollout. Image uploads and tool-based workflows keep their existing limits (OpenAI, September 22, 2026).

What about the GPT-6 Sol thought slider?

The thought slider lets Plus and Pro users set reasoning effort per message: none, low, medium, high, xhigh, or max. Higher effort uses more tokens and costs more per answer but produces fewer step-by-step errors (OpenAI, September 22, 2026).

Is GPT-6 Sol the same price as GPT-6 Astra?

Yes - both list at $5 input and $30 output per million tokens.

The difference is that GPT-6 Sol has cached input pricing ($0.20 per million), while Astra does not. For workflows with significant prompt-caching, Sol becomes cheaper in practice; for one-off requests, the two models are equivalent in price (OpenAI API pricing, September 22, 2026).

Where can I read the GPT-6 Sol system card?

OpenAI has not yet published a separate system card for GPT-6 Sol. The September 22 announcement references GPT-6 Astra's system card for safety and preparedness details; expect a Sol-specific follow-up over the coming weeks (OpenAI, September 22, 2026).