GPT-5.6 Sol vs Terra vs Luna: Monthly Cost and Routing Guide

Decision first: start most production traffic on GPT-5.6 Terra, escalate only the difficult failures to Sol, and route repeatable high-volume work to Luna. At 10 million input and 2 million output tokens per month, the tracked-rate scenarios are $110 for Sol, $55 for Terra, and $22 for Luna. Sol must recover its premium through more accepted hard tasks; Luna wins only when its lower tier remains reliable. Current provider quotes remain on the linked model-detail pages; this guide compares monthly routing outcomes.

GPT-5.6 tier	Input / 1M	Output / 1M	Monthly scenario	Routing role	Current evidence
GPT-5.6 Sol	$5 tracked	$30 tracked	$110	Difficult frontier tasks and escalation	Current Sol providers and source status
GPT-5.6 Terra	$2.50 tracked	$15 tracked	$55	Default balanced production route	Current Terra providers and source status
GPT-5.6 Luna	$1 tracked	$6 tracked	$22	Repeatable, high-volume work	Current Luna providers and source status

Prices are a ComputeUnion snapshot. Open the linked model page to verify the latest source, provider availability, and update time before purchasing.

How OpenAI positions Sol, Terra, and Luna

OpenAI’s current model guidance describes GPT-5.6 Sol as the frontier tier, Terra as the balance of intelligence and cost, and Luna as the efficient tier. See OpenAI’s GPT-5.6 model guidance.

The current ComputeUnion price snapshot is $5/$30 for Sol, $2.50/$15 for Terra, and $1/$6 for Luna per million input/output tokens.

External Capability Snapshot

Model	Artificial Analysis Intelligence Index	Configuration	Checked
GPT-5.6 Sol	59	max	2026-07-11
GPT-5.6 Terra	55	max	2026-07-11
GPT-5.6 Luna	51	max	2026-07-11

These scores are a dated external benchmark reference, not a universal quality verdict. Use the model pages to inspect the source and compare price, provider coverage, and workload fit.

What each additional capability point costs in this snapshot

A simple cost-to-index ratio is not a universal value score, but it makes the trade-off visible. Under the same monthly workload, Luna costs about $0.43 per Intelligence Index point, Terra $1.00 and Sol $1.86. Sol therefore needs to solve the difficult work that Terra or Luna cannot; otherwise its higher tier is wasted spend.

Model	Monthly scenario	Intelligence Index	Cost / index point	What must be true
GPT-5.6 Sol	$110	59	$1.86	Frontier tasks materially improve
GPT-5.6 Terra	$55	55	$1.00	Balanced quality is sufficient
GPT-5.6 Luna	$22	51	$0.43	High-volume tasks remain reliable

The ratio combines a dated external score with a ComputeUnion cost scenario only to expose the trade-off. It is not a new benchmark and should not replace testing on your own tasks.

Monthly cost for the three GPT-5.6 tiers

The model-detail pages own current provider quotes and source status. This guide uses one fixed workload—10 million input and 2 million output tokens per month—to show the routing trade-off. It does not assume cache savings, retries, reasoning effort, or channel markups.

For 10 million input tokens and 2 million output tokens per month:

Model	Input cost	Output cost	Estimated monthly total
GPT-5.6 Sol	$50	$60	$110
GPT-5.6 Terra	$25	$30	$55
GPT-5.6 Luna	$10	$12	$22

These totals are workload scenarios based on the tracked token rates above; retries, reasoning effort, caching, and channel markups can change the final bill.

Why Total Cost Matters More Than Launch Price

Total API cost = input tokens + output tokens + reasoning and tool loops + retries − cache savings

Agent workflows may call tools, validate results, and retry failed steps. Their output cost can exceed what a simple input-price comparison suggests.

The official API vs relay pricing decision adds another cost layer. Relay quotes may be lower, but the lowest displayed price is not automatically the best production choice. Check:

• Price source and last update
• Current model availability
• Latency and rate limits
• Payment and support terms
• Retry and failure rates

Use ComputeUnion’s official-versus-relay pricing digest to compare broader price gaps.

For OpenAI context-window data, current model coverage, and source evidence, see the OpenAI platform page.

Who Should Wait Before Switching

Keep the current model and run a controlled evaluation first if:

• GPT-5.5 already meets your needs
• You have not measured Sol, Terra, or Luna on the same production tasks
• Provider availability, latency, or rate limits are still unclear
• Migration cost is larger than the expected token savings

Do not switch only because a model is newer; compare task quality and total cost on the same workload.

Which GPT-5.6 tier should receive each task?

Start with Terra if:

• You need a general production default with balanced capability and cost.
• You have not yet measured which tasks truly require Sol.

Escalate to Sol if:

• Difficult reasoning, coding, or agent tasks fail on Terra often enough to justify the premium.
• The value of an accepted result matters more than minimizing token spend.

Route to Luna if:

• Classification, extraction, transformation, or repeatable tasks remain reliable on the efficient tier.
• High request volume makes the $22 monthly scenario materially better than Terra's $55 baseline.

Only after this internal family routing works should a team run a broader cross-vendor evaluation. Claude Fable 5 remains a higher-cost external alternative in the same workload scenario, but it should win on accepted hard tasks before it displaces the GPT-5.6 routing policy.

Clear Conclusion

Start with Terra. Escalate individual hard tasks to Sol, and route repeatable high-volume work to Luna.

That is more defensible than running every request on the most expensive tier. Claude Fable 5 remains the higher-cost alternative in this scenario and should win a controlled task test before it wins the budget. Provider choice is a separate decision: compare exact model IDs, source status, limits and support before choosing an official API or relay route.

Compare Before You Buy

1. GPT-5.6 Sol current providers and source status
2. GPT-5.6 Terra current providers and source status
3. GPT-5.6 Luna current providers and source status
4. OpenAI platform evidence and model coverage
5. LLM monthly cost calculator

Author: yego | Data sources: ComputeUnion price tracking, OpenAI model guidance, and Artificial Analysis capability references. Last updated: July 14, 2026.