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GPT-5.5 vs GPT-5.6 Terra

GPT-5.5 leads GPT-5.6 Terra on coding, 71.3 to 63.9 on the Vibe Coding Index, and GPT-5.6 Terra costs 2.5x less per output token ($12.00 vs $30.00 per million). Updated October 22, 2026; 120 benchmarks have a result for both.

Replace GPT-5.5 Replace GPT-5.6 Terra
GPT-5.5OpenAI
Coding
71.3
Overall
69.2
Output $/M
$30.00
81
GPT-5.6 TerraOpenAI
Coding
63.9
Overall
68.1
Output $/M
$12.00
38
vs boards won of 120 shared, 1 tied

GPT-5.5 or GPT-5.6 Terra: which to pick

Pick GPT-5.5 for coding: it scores 71.3 on the Vibe Coding Index against 63.9 for GPT-5.6 Terra, though on 5 benchmarks against 6.

Pick GPT-5.6 Terra for output tokens 2.5x cheaper ($12.00 vs $30.00 per million) and a lower cost per solved task ($0.42 against $1.65).

Model AGPT-5.5OpenAI71.3/1005 independent benchmarks$1.65 per solved taskModel BGPT-5.6 TerraOpenAI63.9/1006 independent benchmarks$0.42 per solved task
Shared results
120
GPT-5.5 only
14
GPT-5.6 Terra only
7
Like-for-like categories
8 of 9

Only benchmarks that tested both models count toward a pick; a result only one model has is shown but not compared.

Which one for your work

Each card is decided by one number both models carry. Where only one has it, the card says so and makes no call.

At a glance

Coding index
GPT-5.5 71.3 from 5 benchmarks, GPT-5.6 Terra 63.9 from 6 benchmarks.
Widest category
Math, 8.1 points apart on average over 6 shared benchmarks.
Widest single gap
Kagi LLM Benchmark: GPT-5.5 88.8% against GPT-5.6 Terra 51.3%, 37.5 points apart on a 0 to 100 scale.
Output price
GPT-5.5 $30.00 against GPT-5.6 Terra $12.00 per million output tokens, 2.5x apart.
Context window
Both take 1.05M tokens.

Benchmark by benchmark

First the score: boards each model leads, per category, where both have a result. Then every board, a category to a fold; bars are each result on a 0 to 100 scale, so compare the two in a row, not one row with another.

Boards won, where both have a result
CategoryGPT-5.5BarsGPT-5.6 TerraTies
Coding7121 tie
Intelligence02
Agentic work712
Reasoning143
Math33
Knowledge111
Web design72
General323
All shared boards81381 tie
CodingLike-for-likeSix of these boards feed the Vibe Coding Index712
Coding benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
LiveBench coding85.1%86.2%GPT-5.6 Terra
LMArena WebDev15131522GPT-5.6 Terra
AA Coding Index74.976.7GPT-5.6 Terra
LiveCodeBench (Vals AI)85.3%85.9%GPT-5.6 Terra
SWE-bench Verified (Vals AI)82.6%95.4%GPT-5.6 Terra
Terminal-Bench 4 (Vals AI)Not measured22.7%Only GPT-5.6 Terra measured
Vibe Code Bench (Vals AI)69.8%74.6%GPT-5.6 Terra
Code migration (Vals AI)45.2%47.8%GPT-5.6 Terra
ProgramBench (Vals AI)0.5%0.5%Tie
IOI (Vals AI)Not measured87.6%Only GPT-5.6 Terra measured
Terminal-Bench 2.1 (Vals AI)76.4%77.5%GPT-5.6 Terra
Vibe Code Bench 1-100 (Vals AI)Not measured14.8%Only GPT-5.6 Terra measured
SkillsBench (Vals AI)62.5%58.9%GPT-5.5
CyberBench (Vals AI)Not measured72.1%Only GPT-5.6 Terra measured
SciCode56.1%55.0%GPT-5.5
Terminal-Bench Hard (Artificial Analysis run)60.6%62.9%GPT-5.6 Terra
Terminal-Bench84.7%Not measuredOnly GPT-5.5 measured
FrontierCode43.0%41.3%GPT-5.5
GSO-Bench40.2%Not measuredOnly GPT-5.5 measured
WeirdML84.9%78.3%GPT-5.5
MirrorCode10.0%Not measuredOnly GPT-5.5 measured
ALE-Bench1943.01951.4GPT-5.6 Terra
LMArena Text: coding14941485GPT-5.5
LMArena Text: software and IT14931482GPT-5.5
LMArena WebDev: React15061513GPT-5.6 Terra
LMArena WebDev: HTML15431526GPT-5.5
LMArena WebDev: from an image15321541GPT-5.6 Terra
SciCodeNot measured10.8%Only GPT-5.6 Terra measured
Neither model has a result on the other 11 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index02
Intelligence benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
AA Intelligence Index38.442.1GPT-5.6 Terra
Epoch Capabilities Index159.7160.1GPT-5.6 Terra
Agentic workLike-for-likePublic boards, shown as published, kept out of the index712
Agentic work benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
AA Agentic Index36.443.2GPT-5.6 Terra
Design Arena: agents building web apps11171120GPT-5.6 Terra
Design Arena: agents building full-stack apps10891061GPT-5.5
Design Arena: agents building mobile apps11421111GPT-5.5
Design Arena: agents building Android apps11641062GPT-5.5
Design Arena: agents building Godot games1173Not measuredOnly GPT-5.5 measured
Design Arena: agents building games11791083GPT-5.5
Design Arena: HTML slides10171058GPT-5.6 Terra
Design Arena: PowerPoint slides10841105GPT-5.6 Terra
LiveBench research61.6%60.4%GPT-5.5
LiveBench browser48.0%84.0%GPT-5.6 Terra
LiveBench long agentic44.6%48.4%GPT-5.6 Terra
SREBench (Vals AI)3.8%9.5%GPT-5.6 Terra
Finance Agent (Vals AI)51.8%54.4%GPT-5.6 Terra
Tax Agent Bench (Vals AI)21.8%30.0%GPT-5.6 Terra
Legal Research Bench (Vals AI)40.4%41.4%GPT-5.6 Terra
Excel Modeling Benchmark (Vals AI)64.5%66.2%GPT-5.6 Terra
Terminal-Bench-Science (Vals AI)Not measured10.0%Only GPT-5.6 Terra measured
Time Horizon Index (Vals AI)8.3%Not measuredOnly GPT-5.5 measured
τ²-Bench Telecom93.9%86.3%GPT-5.5
APEX-Agents55.1%58.2%GPT-5.6 Terra
Remote Labor Index6.3%Not measuredOnly GPT-5.5 measured
OSWorld 2.013.0%Not measuredOnly GPT-5.5 measured
BALROGNot measured53.2%Only GPT-5.6 Terra measured
DeepResearch Bench54.0%Not measuredOnly GPT-5.5 measured
PostTrainBench27.2%Not measuredOnly GPT-5.5 measured
Vending-Bench 2$7,524$7,343GPT-5.5
Neither model has a result on the other 14 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index143
Reasoning benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
GPQA Diamond93.2%90.9%GPT-5.5
LiveBench reasoning89.7%90.6%GPT-5.6 Terra
MMMU Pro (Vals AI)88.3%86.5%GPT-5.5
GPQA Diamond (Artificial Analysis run)93.5%92.5%GPT-5.5
Humanity's Last Exam (Artificial Analysis run)45.8%42.9%GPT-5.5
GPQA Diamond (Epoch AI run)90.7%93.3%GPT-5.6 Terra
ARC-AGI95.0%96.5%GPT-5.6 Terra
ARC-AGI-285.0%83.9%GPT-5.5
SimpleBench69.0%48.9%GPT-5.5
Chess puzzles63.0%47.0%GPT-5.5
Mystery game puzzles56.0%35.0%GPT-5.5
EBR-bench34.3%Not measuredOnly GPT-5.5 measured
LMArena Text: hard prompts14891469GPT-5.5
LMArena Text: expert15071496GPT-5.5
LMArena Text: hard prompts in English14831465GPT-5.5
LMArena Vision: diagrams13251295GPT-5.5
LMArena Vision: homework13321312GPT-5.5
Kagi LLM Benchmark88.8%51.3%GPT-5.5
Neither model has a result on the other 4 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index33
Math benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
OTIS Mock AIME84.4%99.7%GPT-5.6 Terra
FrontierMath, tiers 1 to 385.3%86.0%GPT-5.6 Terra
FrontierMath, tier 472.5%70.7%GPT-5.5
ProofBench50.0%74.0%GPT-5.6 Terra
LMArena Text: math14871465GPT-5.5
LMArena Text: mathematical work14961478GPT-5.5
Neither model has a result on the other 7 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index111
Knowledge benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
MMLU Pro88.1%86.7%GPT-5.5
LegalBench (Vals AI)86.5%85.1%GPT-5.5
CaseLaw (Vals AI)66.2%Not measuredOnly GPT-5.5 measured
CorpFin (Vals AI)68.4%65.3%GPT-5.5
TaxEval (Vals AI)75.0%76.2%GPT-5.6 Terra
MortgageTax (Vals AI)68.8%67.3%GPT-5.5
MedCode (Vals AI)49.1%43.4%GPT-5.5
SimpleQA Verified63.0%43.2%GPT-5.5
LMArena Text: science14851452GPT-5.5
LMArena Text: medicine and healthcare14651430GPT-5.5
LMArena Text: legal and government14911461GPT-5.5
LMArena Text: business and finance14781448GPT-5.5
FACTS Benchmark Suite66.7%52.0%GPT-5.5
Neither model has a result on the other 5 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index72
Web design benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
Design Arena: websites12561268GPT-5.6 Terra
Design Arena: UI components12571256GPT-5.5
Design Arena: game dev12931229GPT-5.5
Design Arena: data viz12641240GPT-5.5
Design Arena: 3D11971134GPT-5.5
Design Arena: all code categories12601241GPT-5.5
Design Arena: SVG12341219GPT-5.5
Design Arena: ASCII art12551177GPT-5.5
LiveBench design70.3%76.0%GPT-5.6 Terra
GeneralLike-for-likePublic boards, shown as published, kept out of the index323
General benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
LiveBench data analysis81.6%79.3%GPT-5.5
Public Benefits Bench (Vals AI)60.9%62.4%GPT-5.6 Terra
SAGE (Vals AI)51.5%47.0%GPT-5.5
MedScribe (Vals AI)86.9%82.9%GPT-5.5
Vals Multimodal Index68.1%65.1%GPT-5.5
IFBench75.9%71.2%GPT-5.5
Long context reasoning (AA-LCR)84.3%83.0%GPT-5.5
DTBench96.0%93.3%GPT-5.5
LMCA54.3%54.9%GPT-5.6 Terra
Surface Evolver Bench88.1%83.8%GPT-5.5
Furniture assembly44.2%54.2%GPT-5.6 Terra
ExploitBench47.4%Not measuredOnly GPT-5.5 measured
CL-bench Life22.2%Not measuredOnly GPT-5.5 measured
LMArena Text14711448GPT-5.5
LMArena Text: instruction following14781456GPT-5.5
LMArena Text: creative writing14551413GPT-5.5
LMArena Vision12971271GPT-5.5
LMArena Text: English14701449GPT-5.5
LMArena Text: non-English14671441GPT-5.5
LMArena Text: Chinese15341514GPT-5.5
LMArena Text: German14801460GPT-5.5
LMArena Text: Japanese14991454GPT-5.5
LMArena Text: Korean14601427GPT-5.5
LMArena Text: French14851466GPT-5.5
LMArena Text: Spanish14681451GPT-5.5
LMArena Text: Russian14731452GPT-5.5
LMArena Text: Polish14651446GPT-5.5
LMArena Text: multi-turn14761453GPT-5.5
LMArena Text: longer queries14841454GPT-5.5
LMArena Text: writing and language14661431GPT-5.5
LMArena Text: entertainment and media14491418GPT-5.5
LMArena Vision: English12921272GPT-5.5
LMArena Vision: Chinese13601337GPT-5.5
LMArena Vision: reading text13061278GPT-5.5
LMArena Vision: humor12931236GPT-5.5
LMArena Vision: recognizing things1231Not measuredOnly GPT-5.5 measured
LMArena Vision: creative writing13011248GPT-5.5
LMArena Document14861472GPT-5.5
Neither model has a result on the other 8 boards here
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
Image generation benchmarks for GPT-5.5 and GPT-5.6 Terra
BenchmarkGPT-5.5GPT-5.6 TerraLeader
Neither model has a result on 5 boards here

What each workload costs

Three fixed token mixes at each model's listed price, so per-token rates become a bill.

Chat turn

1K input + 500 output tokens

GPT-5.5$0.020Fits in one request
GPT-5.6 Terra$0.0080Fits in one request

GPT-5.6 Terra costs less

Repository review

50K input + 3K output tokens

GPT-5.5$0.340Fits in one request
GPT-5.6 Terra$0.136Fits in one request

GPT-5.6 Terra costs less

Agent loop

200K input + 10K output tokens

GPT-5.5$1.30Fits in one request
GPT-5.6 Terra$0.520Fits in one request

GPT-5.6 Terra costs less

Listed OpenRouter rates, without cache or batch discounts. A workload that does not fit a model's context window would need splitting.

Specification differences

The leading value in a row is marked; a row with a missing value names no leader. Our two rows are marked in red.

Specifications of GPT-5.5 and GPT-5.6 Terra
SpecificationOpenAI GPT-5.5OpenAI GPT-5.6 Terra
MakerOpenAIOpenAI
WeightsNo public weights listedNo public weights listed
ReleasedApril 24, 2026July 9, 2026
Context window1.05M1.05M
Input $/Mtok$5.00$2.00
Output $/Mtok$30.00$12.00
Coding index71.363.9
Independent measurements behind it56
Cost per solved task$1.65$0.42
SourceOpenRouter listingOpenRouter listing

Questions

Is GPT-5.5 better than GPT-5.6 Terra for coding?

Pick GPT-5.5 for coding: it scores 71.3 on the Vibe Coding Index against 63.9 for GPT-5.6 Terra, though on 5 benchmarks against 6. Pick GPT-5.6 Terra for output tokens 2.5x cheaper ($12.00 vs $30.00 per million) and a lower cost per solved task ($0.42 against $1.65).

Which is cheaper, GPT-5.5 or GPT-5.6 Terra?

GPT-5.5 costs $5.00 per million input tokens and $30.00 per million output tokens; GPT-5.6 Terra costs $2.00 and $12.00. Per solved SWE-bench Verified task, GPT-5.5 costs $1.65 and GPT-5.6 Terra $0.42.

Which has the bigger context window, GPT-5.5 or GPT-5.6 Terra?

Neither: both take 1.05M tokens.

How many benchmarks is the GPT-5.5 vs GPT-5.6 Terra comparison based on?

120 benchmarks have a result for both models as of October 22, 2026. GPT-5.5's coding index rests on 5 independent benchmarks and GPT-5.6 Terra's on 6. Where only one model has a result, the page says so instead of naming a winner.

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