Compare GPT-4 Turbo and GPT-5.6 Terra: Cut Costs 4x with Next-Gen Intelligence
GPT-4 Turbo vs GPT-5.6 Terra: which should I use?
Migrating from legacy GPT-4 Turbo ($10.00/$30.00 per million tokens) to GPT-5.6 Terra ($2.50/$15.00 per million tokens) cuts token costs by up to 75% while expanding context from 128K to 1M tokens. Verified 2026-09-07.
Verified 2026-09-07
Where can you find price, speed, and task evidence for GPT-4 Turbo and GPT-5.6 Terra?
Which tasks fit GPT-4 Turbo and GPT-5.6 Terra?
Best-fit task signals from the published model strengths; this is not a substitute for a controlled benchmark.
| Fact | GPT-4 Turbo | GPT-5.6 Terra |
|---|---|---|
| Best fit | Legacy high-precision tasks superseded by GPT-5.6 Terra. | Legacy GPT-5.6 balanced-tier workloads superseded by GPT-6 Sol. |
| Reasoning mode | Unavailable | Available |
What does a Coding Agent workload cost with GPT-4 Turbo and GPT-5.6 Terra?
Modeled for Coding Agent: 20,000 input + 2,000 output tokens per task, 1 turn. This is a workload model, not a provider quote.
| Fact | GPT-4 Turbo | GPT-5.6 Terra |
|---|---|---|
| Coding Agent / task | $0.26 (modeled) | $0.08 (modeled) (winner) |
| Input / output rate | $10.00 / $30.00 per M | $2.50 / $15.00 per M |
How fast are GPT-4 Turbo and GPT-5.6 Terra?
Only non-estimated benchmark results are shown as measured.
| Fact | GPT-4 Turbo | GPT-5.6 Terra |
|---|---|---|
| Measured throughput | Unavailable | 78 tokens/s |
| Time to first token | Unavailable | 380 ms |
How compatible are GPT-4 Turbo and GPT-5.6 Terra with APIs?
Provider-level wire-format and SDK facts; model-specific parameter differences may still apply.
| Fact | GPT-4 Turbo | GPT-5.6 Terra |
|---|---|---|
| OpenAI SDK | Usable | Usable |
| Request shape | Canonical /chat/completions and /responses shape — every OpenAI-compatible provider on this site imitates it. | Canonical /chat/completions and /responses shape — every OpenAI-compatible provider on this site imitates it. |
| Streaming | SSE (OpenAI delta) | SSE (OpenAI delta) |
What are the privacy and retention policies for GPT-4 Turbo and GPT-5.6 Terra?
Provider policy and residency facts from the verified provider registry. A missing retention policy is not treated as a guarantee.
| Fact | GPT-4 Turbo | GPT-5.6 Terra |
|---|---|---|
| Provider says API data trains models | No | No |
| Published retention period | Unavailable | Unavailable |
| Data residency | US by default; EU data residency available on enterprise agreements | US by default; EU data residency available on enterprise agreements |
How much effort does it take to migrate between GPT-4 Turbo and GPT-5.6 Terra?
Direction is from each displayed model to the other. Effort is derived from provider compatibility and published parameter maps.
| Fact | GPT-4 Turbo | GPT-5.6 Terra |
|---|---|---|
| Move GPT-4 Turbo → GPT-5.6 Terra | drop-in; 0 breaking parameter differences | Target: GPT-5.6 Terra |
| Move GPT-5.6 Terra → GPT-4 Turbo | Source: GPT-5.6 Terra | drop-in; 0 breaking parameter differences |
| Why | Same provider; only the model identifier changes. | Same provider; only the model identifier changes. |
Exact-pair cutover and operating-tier guide. Verified 2026-09-02. The three sections below are computed from dated scenarios; assumptions and unavailable joins are not observations.
Exact pair boundary: OpenAI; legacy snapshot and Terra exact ID required; no alias-based equivalence. Requested models are gpt-4-turbo and gpt-5.6-terra. Provider, rate, pricing, and task pages remain fact owners.
Legacy-to-Responses compatibility register
Frozen scenario board. Formula / deterministic rule: compatible = field mapping + parser assertion + stop/usage behavior join; unresolved required semantic => fail closed Boundary: Exact GPT-4 Turbo-to-Terra response modernization; code walkthroughs and standalone API contracts remain elsewhere.
| Frozen scenario | Pair, host, surface, and evidence fields | Result | State |
|---|---|---|---|
| system message | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; version=legacy-001; instruction mapping=required; prompt hash=turbo-terra-001; output field=required; evidence=2026-09-02 | Map system content to the target instruction field only after response equivalence is asserted. | CONDITIONAL — adapter assertion |
| stop sequence | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; version=legacy-002; stop value=declared; stop reason=required; parser assertion=missing; evidence=2026-09-02 | Unavailable — stop behavior and parser assertion are not joined | UNAVAILABLE — stop semantics |
| JSON object | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; schema=json-object-003; schema hash=required; refusal behavior=required; validator version=required; evidence=2026-09-02 | Unavailable — refusal and validation behavior are not paired | UNAVAILABLE — JSON contract |
| strict schema | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; schema=strict-004; schema hash=strict-004; output parser=versioned; result hash=missing; evidence=2026-09-02 | Require field-level parser tests before enabling strict output. | CONDITIONAL — parser test |
| function call | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; tool schema=function-005; call ID/arguments/result IDs=required; tool side effects=read-only; evidence=2026-09-02 | Unavailable — tool-call field mapping is not evidenced | UNAVAILABLE — tool register |
| streamed usage | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; stream=usage-006; event sequence hash=required; final usage field=required; client parser=versioned; evidence=2026-09-02 | Unavailable — stream usage settlement is missing | UNAVAILABLE — stream usage |
First-party provenance: OpenAI Responses API; verification date 2026-09-02. Missing or conflicting joins fail closed.
128K-to-Terra workload-envelope receipt
Frozen scenario board. Formula / deterministic rule: admit = input components + reasoning/output/tool reserve ≤ documented cap; unknown tokenizer or cap => Unavailable Boundary: A requested token count does not prove usable recall, and this module does not own a general context-window ranking.
| Frozen scenario | Pair, host, surface, and evidence fields | Result | State |
|---|---|---|---|
| 32K chat | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; envelope=32k-001; input=32K; tokenizer owner=required; output/reasoning/tool reserve=declared; cap=dated; evidence=2026-09-02 | Calculate remaining reserve only after both exact cap joins. | CONDITIONAL — cap join |
| 110K report | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; envelope=110k-002; input=110K; output reserve=4K; reasoning reserve=required; segmentation=planned; evidence=2026-09-02 | Unavailable — Terra usable reserve and tokenizer estimate are not joined | UNAVAILABLE — long-input join |
| 150K repository | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; envelope=repo-003; repository hash=repo-003; tokenizer=required; tool reserve=declared; retrieval depth=required; evidence=2026-09-02 | Segment only with dependency-safe retrieval and artifact hashes. | CONDITIONAL — segmentation probe |
| 500K corpus | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; envelope=corpus-004; corpus hash=corpus-004; input estimate=required; output/tool reserve=declared; cap=exact; evidence=2026-09-02 | Unavailable — documented admission and retained-span evidence are missing | UNAVAILABLE — over-envelope evidence |
| image-plus-text | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; envelope=media-005; image artifact=media-005; image units=required; text tokens=required; output reserve=declared; evidence=2026-09-02 | Unavailable — media-unit accounting is not evidenced for the pair | FAIL CLOSED — media accounting |
| unknown token count | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Chat Completions / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; envelope=unknown-006; tokenizer owner=missing; input/output reserve=unknown; segmentation=unknown; evidence=2026-09-02 | Reject or measure before submitting; never equate unknown with zero. | BLOCKED — estimate missing |
First-party provenance: OpenAI model documentation; verification date 2026-09-02. Missing or conflicting joins fail closed.
Terra cutover canary and rollback ledger
Frozen scenario board. Formula / deterministic rule: promote = matched hashes + acceptance/schema/tool/latency/token gates + sample floor + fallback ready Boundary: Launch claims do not promote a production route; this is the exact GPT-4 Turbo/Terra release decision.
| Frozen scenario | Pair, host, surface, and evidence fields | Result | State |
|---|---|---|---|
| FAQ | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Responses / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; cohort=canary-001; prompt/config/result hashes=paired; acceptance rubric=declared; sample floor=required; fallback=turbo; evidence=2026-09-02 | Unavailable — paired acceptance observations are absent | HOLD — FAQ cohort |
| document analysis | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Responses / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; cohort=canary-002; artifact hash=doc-002; citations=required; long-input reserve=required; output hash=missing; evidence=2026-09-02 | Unavailable — document acceptance and envelope evidence are missing | HOLD — document gate |
| code review | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Responses / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; cohort=canary-003; repository/test hashes=paired; tool schema=required; tests+review floor=declared; attempt cap=2; evidence=2026-09-02 | Unavailable — paired patch acceptance is not measured | HOLD — code gate |
| tool workflow | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Responses / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; cohort=canary-004; tool trace/schema hashes=paired; side_effects=contained; idempotency=required; latency gate=declared; evidence=2026-09-02 | Unavailable — tool and latency telemetry are absent | HOLD — tool gate |
| long-context retrieval | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Responses / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; cohort=canary-005; corpus/query hashes=paired; evidence depth=declared; output/tool reserve=required; sample floor=required; evidence=2026-09-02 | Unavailable — retrieval evidence and sample floor are missing | HOLD — long-context gate |
| regression fixture | pair=gpt-4-turbo vs gpt-5.6-terra; provider/host/surface=api.openai.com / api.openai.com; Responses / Responses; requested IDs=gpt-4-turbo,gpt-5.6-terra; effective IDs=gpt-4-turbo,gpt-5.6-terra; cohort=canary-006; baseline hash=turbo; candidate hash=terra; failure class=required; rollback=ready; attempt cap=2; evidence=2026-09-02 | Rollback to GPT-4 Turbo on a critical failure and stop after the attempt cap. | ROLLBACK — baseline retained |
First-party provenance: OpenAI model documentation; verification date 2026-09-02. Missing or conflicting joins fail closed.
Method and limitations: formulas are deterministic; assumptions are labeled; no missing provider, host, account, region, realm, cluster, alias, snapshot, version, artifact, effort, tool, modality, benchmark, workload, rate-period, timestamp, or result is transferred. Run this scenario →
Exact-pair decision guide · verified 2026-09-07
Exact pair boundary: OpenAI; same provider, legacy migration, legacy $10/$30 pricing vs next-gen $2.50/$15.00 tariffs, and 1M context must join. Requested models are gpt-4-turbo and gpt-5.6-terra. Provider, rate, pricing, and task pages remain fact owners.
Legacy maintenance vs Terra upgrade migration ledger
Frozen scenario board. Formula / deterministic rule: savings = turbo_monthly_spend - terra_monthly_spend; up to 75% cost reduction Boundary: Owns upgrade decision modeling and cost savings from GPT-4 Turbo to GPT-5.6 Terra.
| Frozen scenario | Pair, identity, host, surface, and evidence fields | Result | State |
|---|---|---|---|
| 10K legacy enterprise queries | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=10K legacy enterprise queries; workload volume; GPT-4 Turbo spend; GPT-5.6 Terra spend; cost savings; savings percentage; migration status; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — 10K legacy enterprise queries is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| 50K automated pull request reviews | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=50K automated pull request reviews; workload volume; GPT-4 Turbo spend; GPT-5.6 Terra spend; cost savings; savings percentage; migration status; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — 50K automated pull request reviews is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| 100K data extraction tasks | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=100K data extraction tasks; workload volume; GPT-4 Turbo spend; GPT-5.6 Terra spend; cost savings; savings percentage; migration status; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — 100K data extraction tasks is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| prompt caching active (Terra 50% read discount) | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=prompt caching active (Terra 50% read discount); workload volume; GPT-4 Turbo spend; GPT-5.6 Terra spend; cost savings; savings percentage; migration status; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — prompt caching active (Terra 50% read discount) is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| batch queue workload (50% discount) | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=batch queue workload (50% discount); workload volume; GPT-4 Turbo spend; GPT-5.6 Terra spend; cost savings; savings percentage; migration status; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — batch queue workload (50% discount) is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| unresolved parameter mapping | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=unresolved parameter mapping; workload volume; GPT-4 Turbo spend; GPT-5.6 Terra spend; cost savings; savings percentage; migration status; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — unresolved parameter mapping has no matched, dated bilateral observation. | FAIL CLOSED — manual, probe, or source evidence required |
First-party provenance: OpenAI API pricing; verification date 2026-09-07. Missing or conflicting joins fail closed.
Context window expansion (128K to 1M) workload gate
Frozen scenario board. Formula / deterministic rule: eligible = (context <= 128K ? Both : (context <= 1M ? Terra : Excluded)) Boundary: Owns context scaling and capability gating for large inputs.
| Frozen scenario | Pair, identity, host, surface, and evidence fields | Result | State |
|---|---|---|---|
| standard prompt (10K tokens) | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=standard prompt (10K tokens); context size; Turbo eligible; Terra eligible; Turbo cost; Terra cost; workload gate verdict; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — standard prompt (10K tokens) is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| large legal document (64K tokens) | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=large legal document (64K tokens); context size; Turbo eligible; Terra eligible; Turbo cost; Terra cost; workload gate verdict; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — large legal document (64K tokens) is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| maximum Turbo context (128K boundary) | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=maximum Turbo context (128K boundary); context size; Turbo eligible; Terra eligible; Turbo cost; Terra cost; workload gate verdict; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — maximum Turbo context (128K boundary) is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| repository dump (250K tokens) | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=repository dump (250K tokens); context size; Turbo eligible; Terra eligible; Turbo cost; Terra cost; workload gate verdict; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — repository dump (250K tokens) is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| 1M full context analysis | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=1M full context analysis; context size; Turbo eligible; Terra eligible; Turbo cost; Terra cost; workload gate verdict; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — 1M full context analysis is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| unsupported context request | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=unsupported context request; context size; Turbo eligible; Terra eligible; Turbo cost; Terra cost; workload gate verdict; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — unsupported context request has no matched, dated bilateral observation. | FAIL CLOSED — manual, probe, or source evidence required |
First-party provenance: OpenAI model documentation; verification date 2026-09-07. Missing or conflicting joins fail closed.
Parameter mapping and backward compatibility verification
Frozen scenario board. Formula / deterministic rule: migration_risk = (unsupported_params > 0 ? ManualReview : AutoApproved) Boundary: Owns compatibility verification and smooth cutover.
| Frozen scenario | Pair, identity, host, surface, and evidence fields | Result | State |
|---|---|---|---|
| standard temperature & max_tokens payload | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=standard temperature & max_tokens payload; payload configuration; Turbo compatible; Terra compatible; migration risk; cutover readiness; migration recommendation; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — standard temperature & max_tokens payload is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| tool_choice and json_schema structured outputs | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=tool_choice and json_schema structured outputs; payload configuration; Turbo compatible; Terra compatible; migration risk; cutover readiness; migration recommendation; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — tool_choice and json_schema structured outputs is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| deprecated seed and logit_bias parameters | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=deprecated seed and logit_bias parameters; payload configuration; Turbo compatible; Terra compatible; migration risk; cutover readiness; migration recommendation; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — deprecated seed and logit_bias parameters is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| system prompt behavior verification | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=system prompt behavior verification; payload configuration; Turbo compatible; Terra compatible; migration risk; cutover readiness; migration recommendation; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — system prompt behavior verification is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| rate limit quota saturation | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=rate limit quota saturation; payload configuration; Turbo compatible; Terra compatible; migration risk; cutover readiness; migration recommendation; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — rate limit quota saturation is a frozen fixture pending exact identity, configuration, and denominator joins. | UNTESTED — assumption cannot establish a verdict |
| unsupported parameter error | pair=gpt-4-turbo vs gpt-5.6-terra; provider=OpenAI; hostA=api.openai.com; hostB=api.openai.com; surfaceA=OpenAI Responses API; surfaceB=OpenAI Responses API; requested/effective IDs=gpt-4-turbo,gpt-5.6-terra; scenario=unsupported parameter error; payload configuration; Turbo compatible; Terra compatible; migration risk; cutover readiness; migration recommendation; prompt/config/input/output/result/cache/checkpoint/artifact hashes=required; evidence=2026-09-07; measurement versus assumption=explicit | Unavailable — unsupported parameter error has no matched, dated bilateral observation. | FAIL CLOSED — manual, probe, or source evidence required |
First-party provenance: OpenAI API documentation; verification date 2026-09-07. Missing or conflicting joins fail closed.
Method and limitations: formulas are deterministic; observed and assumed inputs are labeled; no missing provider, host, account, region, realm, alias, snapshot, revision, weight, artifact, control, tool, modality, workload, rate-period, timestamp, or result is transferred. Run this scenario →
How do GPT-4 Turbo and GPT-5.6 Terra compare on specs?
| GPT-4 Turbo | GPT-5.6 Terra | |
|---|---|---|
| Price (input) | $10.00/M | $2.50/M ✓ |
| Price (output) | $30.00/M | $15.00/M ✓ |
| Blended price | $15.00/M | $5.63/M ✓ |
| Context window | 128,000 tokens | 1,000,000 tokens ✓ |
| Max output | 4,096 tokens | 128,000 tokens ✓ |
| Modalities | text, vision | text, vision |
| Reasoning mode | No | Yes |
| Released | 2024-04 | 2026-06 |
| Speed | Not measured | 78 t/s |
How much do GPT-4 Turbo and GPT-5.6 Terra cost at scale?
| Tokens / month | GPT-4 Turbo | GPT-5.6 Terra | Delta |
|---|---|---|---|
| 1,000,000 | $15.00 | $5.63 | $9.38 (2.7×) |
| 10,000,000 | $150.00 | $56.25 | $93.75 (2.7×) |
| 100,000,000 | $1500.00 | $562.50 | $937.50 (2.7×) |
Choose GPT-4 Turbo if…
- ✓Pinnacle of GPT-4 era reliability
- ✓High instruction precision
- ✓Vision capability
- ✓Legacy high-precision tasks superseded by GPT-5.6 Terra.
Choose GPT-5.6 Terra if…
- ✓Balanced cost-to-intelligence ratio
- ✓Reasoning mode available on demand
- ✓Same 1M context as Sol
- ✓Legacy GPT-5.6 balanced-tier workloads superseded by GPT-6 Sol.
Run this exact matchup right now
Send the same prompt to GPT-4 Turbo and GPT-5.6 Terra side by side and see the outputs yourself.
Try GPT-4 Turbo vs GPT-5.6 Terra FreeWhat are common questions about GPT-4 Turbo and GPT-5.6 Terra?
Is GPT-4 Turbo cheaper than GPT-5.6 Terra?
GPT-5.6 Terra is cheaper, at $5.63 per million blended tokens vs $15.00 for GPT-4 Turbo.
Which has the bigger context window, GPT-4 Turbo or GPT-5.6 Terra?
GPT-5.6 Terra has the larger context window: 1,000,000 tokens vs 128,000.
Can GPT-4 Turbo replace GPT-5.6 Terra for coding?
Both are viable for coding. Pinnacle of GPT-4 era reliability (GPT-4 Turbo) vs Balanced cost-to-intelligence ratio (GPT-5.6 Terra) — pick based on which strength matters more for your workload.
What related comparisons help choose between GPT-4 Turbo and GPT-5.6 Terra?
Pricing verified 2026-04-06. Specs verified 2026-08-14.