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Head-to-head comparison

GPT-5.6 Terra vs Grok 4.20 Multi-Agent

GPT-5.6 Terra (OpenAI) and Grok 4.20 Multi-Agent (xAI) 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, Grok 4.20 Multi-Agent holds the stronger ModelCap Index position (#18 vs #21); Grok 4.20 Multi-Agent is 4.8× cheaper per output token ($2.50/1M vs $12.00/1M); and Grok 4.20 Multi-Agent offers the longer context window (2M vs 1M tokens).

Which should you choose?

Choose GPT-5.6 Terra if…

  • you want provider choice — 3 listed API providers against 1.
  • Arena coding is your yardstick — 1518 against 1508.
  • you want the more recently listed model — GPT-5.6 Terra was listed 9 July 2026, Grok 4.20 Multi-Agent 31 March 2026.

Choose Grok 4.20 Multi-Agent if…

  • you want the stronger overall ModelCap Index position — #18 against #21 (81.2 vs 79.7 points).
  • API cost matters — $2.50/1M output tokens against $12.00/1M, about 4.8× cheaper.
  • your workload is prompt-heavy — input tokens cost $1.25/1M against $2.00/1M.
  • you need the longer context window — 2M tokens against 1M.

GPT-5.6 Terra vs Grok 4.20 Multi-Agent: specs, pricing and context

Specification comparison of GPT-5.6 Terra and Grok 4.20 Multi-Agent
FieldGPT-5.6 TerraOpenAIGrok 4.20 Multi-AgentxAI
ModelCap Index position#21#18
Index score79.781.2
EvidenceMeasuredMeasured
Input price / 1M tokens$2.00$1.25
Output price / 1M tokens$12.00$2.50
Context window1M tokens2M tokens
Max output tokens128K1.8M
API providers listed31
Weight accessAPI onlyAPI only
Input modalitiesFile, Image, TextText, Image, File
First listed9 July 202631 March 2026
PublisherOpenAIxAI

Evidence: 6 public benchmark observations across 6 boards · 2 public benchmark observations across 2 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: GPT-5.6 Terra vs Grok 4.20 Multi-Agent

Public benchmark boards where GPT-5.6 Terra or Grok 4.20 Multi-Agent has a published result
BoardGPT-5.6 TerraGrok 4.20 Multi-AgentLeads
Arena codingArena (LMArena)15181510–1525X-High15081502–1514Beta · 0309GPT-5.6 Terra
LMArena AgentLMArena1.4%0.3%–2.6%X-High—Only one result
ARC-AGI-2ARC Prize Foundation83.9%Max—Only one result
ARC-AGI-3ARC Prize Foundation0.8%Max—Only one result
AA Intelligence IndexArtificial Analysis42.1intelligence-index:v4.3:max—Only one result
AA τ²-Bench TelecomArtificial Analysis86.3%tau2:telecom:dual-control:pass-at-1:3-repeats:source-model="GPT-5.6 Terra (max)":reasoning=true—Only one result
AA Humanity's Last ExamArtificial Analysis42.9%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GPT-5.6 Terra (max)":reasoning=true—Only one result
Terminal-Bench 4.0Terminal-Bench (Laude Institute)21.5%18.3%–24.8%Codex · Max—Only one result

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.

GPT-5.6 Terra vs Grok 4.20 Multi-Agent: common questions

Is GPT-5.6 Terra better than Grok 4.20 Multi-Agent?

Grok 4.20 Multi-Agent ranks higher on the ModelCap Index as of 22 September 2026: #18 against #21. 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 GPT-5.6 Terra cheaper than Grok 4.20 Multi-Agent?

Grok 4.20 Multi-Agent is cheaper on output tokens: $2.50/1M against $12.00/1M. Input tokens are $2.00/1M for GPT-5.6 Terra and $1.25/1M for Grok 4.20 Multi-Agent. 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 $10.00 for GPT-5.6 Terra versus $3.75 for Grok 4.20 Multi-Agent. Grok 4.20 Multi-Agent costs 62.5% 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, GPT-5.6 Terra or Grok 4.20 Multi-Agent?

Grok 4.20 Multi-Agent has the larger context window: 2M tokens against 1M.

Which is better for coding, GPT-5.6 Terra or Grok 4.20 Multi-Agent?

Arena coding: GPT-5.6 Terra 1518, Grok 4.20 Multi-Agent 1508 — GPT-5.6 Terra leads.

Are GPT-5.6 Terra and Grok 4.20 Multi-Agent open-weight models?

GPT-5.6 Terra: API only. Grok 4.20 Multi-Agent: 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 GPT-5.6 Terra and Grok 4.20 Multi-Agent?

ModelCap currently lists 3 API providers for GPT-5.6 Terra and 1 for Grok 4.20 Multi-Agent, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.

How current is this GPT-5.6 Terra vs Grok 4.20 Multi-Agent 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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