GPT-5.6 Luna Alternatives
Decision and evidence surface verified 2026-08-14.
What is the best alternative to GPT-5.6 Luna?
The closest alternative to GPT-5.6 Luna (OpenAI, $2.25/M blended) is GPT-5.6 Terra, from OpenAI, a drop-in migration priced +150% relative to GPT-5.6 Luna at blended (3:1) rates. There is no meaningful parity loss on this swap.
The closest match to GPT-5.6 Luna (OpenAI, $2.25/M) is GPT-5.6 Terra — a drop-in migration at +150% price.
Ranked — top 8 alternatives
| # | Model | Provider | Effort | Blended $/M (Δ%) | tok/s (Δ%) | Context | Parity | Closeness |
|---|---|---|---|---|---|---|---|---|
| 1 | GPT-5.6 Terra | OpenAI | drop-in | $5.63 (+150%) | -38.1% | 0K | 100% | 86 |
| 2 | GPT-5.6 Sol | OpenAI | drop-in | $8.00 (+255.6%) | -65.1% | 0K | 100% | 83 |
| 3 | Gemini 3.7 Flash | code-change | $1.50 (-33.3%) | — | +49K | 100% | 82 | |
| 4 | Gemini 3.5 Flash Lite | code-change | $0.85 (-62.2%) | +28.6% | 0K | 100% | 75 | |
| 5 | Gemini 3.6 Flash | code-change | $3.00 (+33.3%) | -9.5% | 0K | 100% | 73 | |
| 6 | Gemini 3.1 Pro | code-change | $4.50 (+100%) | -56.3% | +1M | 100% | 71 | |
| 7 | Ministral 8B | Mistral | config | $0.15 (-93.3%) | +25.4% | -744K | 63% | 70 |
| 8 | Mistral Small 3.1 | Mistral | config | $0.26 (-88.3%) | -4% | -744K | 63% | 70 |
Top 3, in detail
Same provider — change the model string, nothing else.
You gain: Max output grows from 64,000 to 128,000 tokens.
base_url: https://api.openai.com/v1 auth: Bearer API key
base_url: https://api.openai.com/v1 auth: Bearer API key sdk: openai model: "gpt-5.6-terra"
Same provider — change the model string, nothing else.
You gain: Max output grows from 64,000 to 128,000 tokens.
base_url: https://api.openai.com/v1 auth: Bearer API key
base_url: https://api.openai.com/v1 auth: Bearer API key sdk: openai model: "gpt-5.6-sol"
contents/parts structure instead of messages; an OpenAI-compatible endpoint exists but only covers a subset of parameters.
You gain: Context grows from 1,000,000 to 1,048,576 tokens; Max output grows from 64,000 to 65,536 tokens.
base_url: https://api.openai.com/v1 auth: Bearer API key
base_url: https://generativelanguage.googleapis.com/v1beta auth: API key (header or query param); OAuth/service-account on Vertex AI sdk: @google/genai model: "gemini-3.7-flash"
Or don't migrate at all
One base URL, one key, change the model string — every alternative above is already callable through All AI Ask.
curl https://allaiask.com/api/v1/chat \
-H "Authorization: Bearer $ALLAIASK_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model": "gpt-5.6-terra", "messages": [{"role": "user", "content": "Hello"}]}'OpenAI gotchas when switching away
- Reasoning tokens are billed separately from output tokens on Sol and Terra.
Related
FAQ
GPT-5.6 Luna stay, acceptance frontier, and protocol replay
Batch 47 decision and evidence surface · verified 2026-08-14 · exact route allowlist match: /alternatives/gpt-5-6-luna.
Luna stay/upgrade/exit compiler
Frozen Batch 47 luna fixture — Exact fast-tier workload contracts and candidate admission gates; first-party evidence checked 2026-08-14; unresolved joins render Unavailable.
Method: every calculation uses only the joined fields shown in its row; missing joins fail closed. First-party source: OpenAI API documentation. Verified: 2026-08-14.
| Fixture / field ID | Named inputs | Observation | Formula / boundary | Decision |
|---|---|---|---|---|
no measured defectbatch47-luna-m1-r1 | source=GPT-5.6 Luna; defect=0; context=64K; tools=strict; evidence=100%; candidate=stay | No measured defect is present; no migration is authorized merely by availability elsewhere. | exit eligible = measured defect ∨ control failure ∨ owned concentration trigger Boundary: No-defect evidence preserves Luna by default. | PASS — stay on Luna. |
64K classification fleet + 120K extractionbatch47-luna-m1-r2 | workload=10K/2K; source context=64K/120K; candidate context=64K/128K; schema=joined; quality=Unavailable | Candidate admits context and schema, but quality floor is not measured for the fleet. | eligible = context ∧ schema ∧ quality floor ∧ critical failures=0 Boundary: Context admission alone cannot authorize a tier move. | UNAVAILABLE — quality frontier missing. |
hard overflow + strict-tool regression + outage/concentrationbatch47-luna-m1-r3 | overflow=120K; tool regression=1; outage=joined; concentration=declared; candidate=Terra/cross-provider | Overflow and tool regression are valid triggers, but each candidate needs its own canary and no vendor-concentration shortcut is inferred. | migration wave = trigger ∧ candidate evidence ∧ rollback owner Boundary: Luna alternatives do not rank the GPT-5.6 family or OpenAI-wide exit. | PASS WITH GATES — canary required. |
High-volume acceptance frontier
Frozen Batch 47 luna fixture — Frozen fleet counts, reviewer budget, retry rules, and observed usage joins; first-party evidence checked 2026-08-14; unresolved joins render Unavailable.
Method: every calculation uses only the joined fields shown in its row; missing joins fail closed. First-party source: OpenAI API documentation. Verified: 2026-08-14.
| Fixture / field ID | Named inputs | Observation | Formula / boundary | Decision |
|---|---|---|---|---|
10,000 classificationsbatch47-luna-m2-r1 | fixture=class-v47; first-pass=9,984; repaired=16; critical failures=0; reviewer minutes=40; coverage=100%; usage=joined | Quality floor and coverage pass on the Luna fixture; repairs are retained as a separate count. | eligible = quality floor met ∧ critical failures=0 ∧ evidence coverage=100% Boundary: This is a Luna fixture result, not a cross-model leaderboard. | PASS — Luna fleet baseline. |
2,000 strict extractions + 1,000 summariesbatch47-luna-m2-r2 | fixture=extract-sum-v47; first-pass=1,968/992; repaired=32/8; critical failures=0/0; reviewer=58m/12m; usage=partial | Acceptance counts pass; usage is joined only for extraction, so no combined token total is emitted. | completion coverage = accepted + repaired / declared; usage total only when every row joins Boundary: Partial usage evidence cannot become a fleet cost calculation. | PASS WITH UNAVAILABLE USAGE — quality scoped. |
500 code edits + 100 four-tool loopsbatch47-luna-m2-r3 | fixture=code-agent-v47; first-pass=471/91; repaired=29/9; critical failures=2/0; reviewer=210m/84m; coverage=100% | Two critical code failures breach the acceptance rule despite complete evidence coverage. | eligible = quality floor met ∧ critical failures=0 ∧ evidence coverage=100% Boundary: Reviewer minutes do not waive a critical failure. | FAIL — migration blocked. |
Luna protocol-and-state replay pack
Frozen Batch 47 luna fixture — Reasoning controls, schemas, tools, context, streams, retries, and caches; first-party evidence checked 2026-08-14; unresolved joins render Unavailable.
Method: every calculation uses only the joined fields shown in its row; missing joins fail closed. First-party source: OpenAI API documentation. Verified: 2026-08-14.
| Fixture / field ID | Named inputs | Observation | Formula / boundary | Decision |
|---|---|---|---|---|
minimal/high/max reasoning controlsbatch47-luna-m3-r1 | model=GPT-5.6 Luna; modes=min/high/max; request IDs=3; effective controls=3; usage IDs=3; checker=pass | All three controls are observed as effective on the source fixture. | control replay pass = request ∧ effective mode ∧ response ∧ usage IDs Boundary: Control evidence is model- and endpoint-specific. | PASS — source contract joined. |
strict schema + forced/parallel tools + 100K contextbatch47-luna-m3-r2 | schema=sha256:77ab; tools=3; event IDs=joined; context=100K; candidate=alternate; template=Unavailable | Source event and tool IDs join; candidate template and effective context are unknown. | replay eligible = identity ∧ schema ∧ tools ∧ context ∧ template Boundary: Candidate-labelled unknowns cannot inherit Luna acceptance. | UNAVAILABLE — candidate template/context missing. |
interrupted stream + cancellation + retry + cached repeatbatch47-luna-m3-r3 | stream=st-42; cancel=joined; retry=rt-42; cache=hit; duplicate effect=0; repair=none | State replay and cached repeat settle with no duplicate effect on the source fixture. | state replay = stream ∧ cancel ∧ retry ∧ cache settlement ∧ duplicate=0 Boundary: No cache behavior is assumed for a destination without usage identity. | PASS — source fixture only. |
Route owner CTA: test this decision path at All AI Ask. This surface does not transfer evidence to another host, model, region, tier, artifact, or scenario.
What is the closest alternative to GPT-5.6 Luna?
GPT-5.6 Terra is the closest match: drop-in migration, +150% price, no significant parity loss.
Can I switch off GPT-5.6 Luna without changing my code?
Within OpenAI, GPT-5.6 Terra is a drop-in swap — same request shape, just change the model string.
What do I lose switching from GPT-5.6 Luna?
Against the closest match, GPT-5.6 Terra, we found no significant parity gap on the dimensions we track.
Prices and specs verified 2026-08-14.