GPT-5.6 Terra vs GPT-5.6 Sol: workhorse or flagship within OpenAI's 2026 lineup?
Default to Terra for production workloads. Pay for Sol only on tasks where Terra's reasoning demonstrably stalls - the 2x input price is real and only earns its keep on hardest-tier reasoning.
Two members of OpenAI's 2026 lineup, one big price gap.
OpenAI's GPT-5.6 family comes in three tiers - Luna (ultra-cheap), Terra (workhorse), and Sol (flagship). Terra and Sol share the same lineage and tooling ecosystem, so the choice is mostly about where in the price-capability curve a workload sits.
By TechCompare · Updated
Cost Comparison
Based on 100,000 input tokens (50% cached), 5,000 output tokens, and 100 requests.Prices are fetched live from OpenRouter and may include temporary promotional discounts not accounted for in our article and comparison figures.
Side-by-side specs
| Spec | GPT-5.6 Terra | GPT-5.6 Sol |
|---|---|---|
| Input Cost (per M) | $2.00 (better on this spec) | $4.00 |
| Output Cost (per M) | $12.00 (better on this spec) | $20.00 |
| Cached Input (per M) | $0.20 (better on this spec) | $0.40 |
| Batch Discount | 50% | 50% |
| Context Window | 1.05M | 1.05M |
How they differ
GPT-5.6 Terra is priced at $2.00 per million input tokens and $12.00 per million output tokens at OpenAI's list price, with a 90% caching discount ($0.20 per million). GPT-5.6 Sol is priced at $4.00 per million input tokens and $20.00 per million output tokens, also with a 90% caching discount ($0.40 per million). Both share the 1.05M context window and 50% batch discount. For a 100K input + 10K output request, Terra costs $0.32 vs Sol's $0.60 - a 2x per-call gap. The decision is whether the workload's reasoning demand actually needs Sol's frontier depth, or whether Terra's workhorse tier covers it. Note: OpenRouter currently runs a limited-time 50% discount that can show Terra at $1/$6 in live calculators.
Verdict
Terra runs $2.00/M input and $12.00/M output against Sol's $4.00 and $20.00, a 2x input and ~1.7x output ratio that holds on cached input at $0.20/M versus $0.40/M. Batch ties at 50% on both and context ties at 1.05M, so neither side has a discount lever to flip. A representative 100K input + 10K output call costs $0.32 on Terra against $0.60 on Sol, which scales to about a $280K gap per million calls. Sol earns back its premium only when its frontier reasoning undoes a Terra retry.
Which should you pick?
Choose GPT-5.6 Terra
High-volume production: chat assistants, RAG, content generation, classification. Terra's list price of $2/$12 makes it the workhorse for everyday OpenAI-stack workloads, and temporary discounts can drop it even lower.
Choose GPT-5.6 Sol
Frontier reasoning where Terra's quality falls short: hard math, deep multi-step planning, complex code synthesis. The 90% cache discount absorbs much of the premium on cache-heavy agentic loops.