Skip to content
ModelCap

Head-to-head comparison

GPT-5.5 vs Grok 4.20 Multi-Agent

GPT-5.5 (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, GPT-5.5 holds the stronger ModelCap Index position (#13 vs #18); Grok 4.20 Multi-Agent is 12× cheaper per output token ($2.50/1M vs $30.00/1M); and Grok 4.20 Multi-Agent offers the longer context window (2M vs 1M tokens).

Which should you choose?

Choose GPT-5.5 if…

  • you want the stronger overall ModelCap Index position — #13 against #18 (82.5 vs 81.2 points).
  • you want provider choice — 3 listed API providers against 1.
  • Arena coding is your yardstick — 1520 against 1508.
  • you want the more recently listed model — GPT-5.5 was listed 24 April 2026, Grok 4.20 Multi-Agent 31 March 2026.

Choose Grok 4.20 Multi-Agent if…

  • API cost matters — $2.50/1M output tokens against $30.00/1M, about 12× cheaper.
  • your workload is prompt-heavy — input tokens cost $1.25/1M against $5.00/1M.
  • you need the longer context window — 2M tokens against 1M.

GPT-5.5 vs Grok 4.20 Multi-Agent: specs, pricing and context

Specification comparison of GPT-5.5 and Grok 4.20 Multi-Agent
FieldGPT-5.5OpenAIGrok 4.20 Multi-AgentxAI
ModelCap Index position#13#18
Index score82.581.2
EvidenceMeasuredMeasured
Input price / 1M tokens$5.00$1.25
Output price / 1M tokens$30.00$2.50
Context window1M tokens2M tokens
Max output tokens128K1.8M
API providers listed31
Weight accessAPI onlyAPI only
Input modalitiesFile, Image, TextText, Image, File
First listed24 April 202631 March 2026
PublisherOpenAIxAI

Evidence: 7 public benchmark observations across 7 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-5.5 vs Grok 4.20 Multi-Agent

Public benchmark boards where GPT-5.5 or Grok 4.20 Multi-Agent has a published result
BoardGPT-5.5Grok 4.20 Multi-AgentLeads
Arena codingArena (LMArena)15201514–1526High15081502–1514Beta · 0309GPT-5.5
LMArena AgentLMArena5.0%4.1%–6.0%X-High—Only one result
ARC-AGI-2ARC Prize Foundation85.0%X-High—Only one result
ARC-AGI-3ARC Prize Foundation0.4%High—Only one result
AA Intelligence IndexArtificial Analysis38.4intelligence-index:v4.3:xhigh—Only one result
AA τ²-Bench TelecomArtificial Analysis93.9%tau2:telecom:dual-control:pass-at-1:3-repeats:source-model="GPT-5.5 (xhigh)":reasoning=true—Only one result
AA Humanity's Last ExamArtificial Analysis45.8%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GPT-5.5 (xhigh)":reasoning=true—Only one result
Terminal-Bench 2.1 Terminus 2Terminal-Bench78.0X-High—Only one result
WildClawBench OpenClawWildClawBench58.2—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-5.5 vs Grok 4.20 Multi-Agent: common questions

Is GPT-5.5 better than Grok 4.20 Multi-Agent?

GPT-5.5 ranks higher on the ModelCap Index as of 22 September 2026: #13 against #18. 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-5.5 cheaper than Grok 4.20 Multi-Agent?

Grok 4.20 Multi-Agent is cheaper on output tokens: $2.50/1M against $30.00/1M. Input tokens are $5.00/1M for GPT-5.5 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 $25.00 for GPT-5.5 versus $3.75 for Grok 4.20 Multi-Agent. Grok 4.20 Multi-Agent costs 85.0% 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, GPT-5.5 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-5.5 or Grok 4.20 Multi-Agent?

Arena coding: GPT-5.5 1520, Grok 4.20 Multi-Agent 1508 — GPT-5.5 leads.

Are GPT-5.5 and Grok 4.20 Multi-Agent open-weight models?

GPT-5.5: 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-5.5 and Grok 4.20 Multi-Agent?

ModelCap currently lists 3 API providers for GPT-5.5 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-5.5 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.

Explore further