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Head-to-head comparison

Claude Sonnet 5 vs GPT-5.6 Terra

Claude Sonnet 5 (Anthropic) and GPT-5.6 Terra (OpenAI) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.

Snapshot as of 22 September 2026

As of 22 September 2026, GPT-5.6 Terra holds the stronger ModelCap Index position (#22 vs #26); and Claude Sonnet 5 is 1.2× cheaper per output token ($10.00/1M vs $12.00/1M).

Which should you choose?

Choose Claude Sonnet 5 if…

  • API cost matters — $10.00/1M output tokens against $12.00/1M, about 1.2× cheaper.
  • you want provider choice — 5 listed API providers against 3.
  • Arena coding is your yardstick — 1520 against 1518.
  • LMArena Agent is your yardstick — 6.0% against 1.4%.

Choose GPT-5.6 Terra if…

  • you want the stronger overall ModelCap Index position — #22 against #26 (79.7 vs 78.5 points).
  • AA Intelligence Index is your yardstick — 42.1 against 38.2.
  • AA Humanity's Last Exam is your yardstick — 42.9% against 41.3%.
  • Terminal-Bench 4.0 is your yardstick — 21.5% against 12.4%.
  • you want the more recently listed model — GPT-5.6 Terra was listed 9 July 2026, Claude Sonnet 5 30 June 2026.

Claude Sonnet 5 vs GPT-5.6 Terra: specs, pricing and context

Specification comparison of Claude Sonnet 5 and GPT-5.6 Terra
FieldClaude Sonnet 5AnthropicGPT-5.6 TerraOpenAI
ModelCap Index position#26#22
Index score78.579.7
EvidenceMeasuredMeasured
Input price / 1M tokens$2.00$2.00
Output price / 1M tokens$10.00$12.00
Context window1M tokens1M tokens
Max output tokens128K128K
API providers listed53
Weight accessAPI onlyAPI only
Input modalitiesText, Image, FileFile, Image, Text
First listed30 June 20269 July 2026
PublisherAnthropicOpenAI

Evidence: 4 public benchmark observations across 4 boards · 6 public benchmark observations across 6 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: Claude Sonnet 5 vs GPT-5.6 Terra

Public benchmark boards where Claude Sonnet 5 or GPT-5.6 Terra has a published result
BoardClaude Sonnet 5GPT-5.6 TerraLeads
Arena codingArena (LMArena)15201513–1527High15181510–1525X-HighClaude Sonnet 5
LMArena AgentLMArena6.0%4.4%–7.6%High1.4%0.3%–2.6%X-HighClaude Sonnet 5
ARC-AGI-2ARC Prize Foundation—83.9%MaxOnly one result
ARC-AGI-3ARC Prize Foundation—0.8%MaxOnly one result
AA Intelligence IndexArtificial Analysis38.2intelligence-index:v4.3:max42.1intelligence-index:v4.3:maxGPT-5.6 Terra
AA τ²-Bench TelecomArtificial Analysis—86.3%tau2:telecom:dual-control:pass-at-1:3-repeats:source-model="GPT-5.6 Terra (max)":reasoning=trueOnly one result
AA Humanity's Last ExamArtificial Analysis41.3%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="Claude Sonnet 5 (Adaptive Reasoning, Max Effort)":reasoning=true42.9%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GPT-5.6 Terra (max)":reasoning=trueGPT-5.6 Terra
Terminal-Bench 4.0Terminal-Bench (Laude Institute)12.4%9.4%–15.5%Claude Code · Max21.5%18.3%–24.8%Codex · MaxGPT-5.6 Terra

Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.

Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.

Claude Sonnet 5 vs GPT-5.6 Terra: common questions

Is Claude Sonnet 5 better than GPT-5.6 Terra?

GPT-5.6 Terra ranks higher on the ModelCap Index as of 22 September 2026: #22 against #26. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.

Is Claude Sonnet 5 cheaper than GPT-5.6 Terra?

Claude Sonnet 5 is cheaper on output tokens: $10.00/1M against $12.00/1M. Input tokens are $2.00/1M for Claude Sonnet 5 and $2.00/1M for GPT-5.6 Terra. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens. For 1,000 requests with 2,000 input and 500 output tokens each (2M input + 0.5M output), the listed-rate estimate is $9.00 for Claude Sonnet 5 versus $10.00 for GPT-5.6 Terra. Claude Sonnet 5 costs 10.0% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.

Which has the bigger context window, Claude Sonnet 5 or GPT-5.6 Terra?

Both publish a 1M-token context window.

Which is better for coding, Claude Sonnet 5 or GPT-5.6 Terra?

Arena coding: Claude Sonnet 5 1520, GPT-5.6 Terra 1518 — Claude Sonnet 5 leads. Terminal-Bench 4.0: Claude Sonnet 5 12.4%, GPT-5.6 Terra 21.5% — GPT-5.6 Terra leads.

Are Claude Sonnet 5 and GPT-5.6 Terra open-weight models?

Claude Sonnet 5: API only. GPT-5.6 Terra: API only. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.

Where can I run Claude Sonnet 5 and GPT-5.6 Terra?

ModelCap currently lists 5 API providers for Claude Sonnet 5 and 3 for GPT-5.6 Terra, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.

How current is this Claude Sonnet 5 vs GPT-5.6 Terra comparison?

Every figure comes from the sealed ModelCap dataset published 22 September 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.

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