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AI Choice Engine

Model comparison

Claude Opus 5.5 vs Grok 4.6

Anthropic against SpaceXAI, compared on context, price, and verified benchmark results.

Catalog record checked September 26, 2026Individual provider fields may changeEvidence confidence: High — see receipts below

Anthropic

Claude Opus 5.5

Frontier

vs

SpaceXAI

Grok 4.6

Frontier

AI model capability comparison
SpecificationClaude Opus 5.5Grok 4.6
ProviderAnthropicSpaceXAI
TierFrontierFrontier
Context windowWinner: 1M500K
Max output128KNot verifiedUnverified
Input / 1M tokens$4Winner: $2
Output / 1M tokens$20Winner: $6
WeightsClosedClosed
ParametersNot disclosedUnverifiedNot disclosedUnverified
Reasoning levelsadaptivelow, medium, high, xhigh
Modalitiestext, imagetext, image
API model idclaude-opus-5-5grok-4.6
ReleasedSeptember 22, 2026August 12, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)57.6Not verifiedUnverified
Artificial Analysis Intelligence Index [high] (2026-09-26)Not verifiedUnverified44.3
Humanity's Last Exam [max] (2026-09-26)61.4Not verifiedUnverified
Terminal-Bench 4.0 [max] (2026-09-26)59.6Not verifiedUnverified
Terminal-Bench 4.0 [xhigh] (2026-09-22)66.4Not verifiedUnverified
Terminal-Bench 2.1 (2026-08-18)Not verifiedUnverified88
GPQA Diamond (2026-08-18)Not verifiedUnverified94.9

Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

  • 2026-09-26
    Artificial Analysis Terminal-Bench 4.0 (independent AA run, part of Intelligence Index v4.3.2)

    Agentic terminal work: long multi-step tasks executed in a sandboxed shell environment.

    Comparable with caveatNOT comparable with Terminal-Bench 2.x or 3.0 — 4.0 uses a new, non-overlapping task set. Within 4.0, scores from different harnesses (tbench.ai agent entries vs Artificial Analysis runs) are not interchangeable.

  • 2026-09-26
    Artificial Analysis Humanity's Last Exam (independent, 2,158 text-only questions)

    Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise.

    Comparable with caveatSubset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.

  • 2026-09-26
    Artificial Analysis

    Composite index blending reasoning, knowledge, and coding evals into one 0–100 score.

    Comparable with caveatOnly same-version scores are comparable. v4.3.2 was rebaselined (the top score fell from 66 on v4.1.1 to ~58), so v4.1.1 figures must not be compared with v4.3.2 figures — check measuredAt.

  • 2026-09-22
    Anthropic — Claude Opus 5.5 announcement (vendor; conflicts with AA's independent 59.6 — harness difference preserved)

    Agentic terminal work: long multi-step tasks executed in a sandboxed shell environment.

    Comparable with caveatNOT comparable with Terminal-Bench 2.x or 3.0 — 4.0 uses a new, non-overlapping task set. Within 4.0, scores from different harnesses (tbench.ai agent entries vs Artificial Analysis runs) are not interchangeable.

  • 2026-08-18
    Artificial Analysis measurement (independent, high effort)

    Agentic terminal work: multi-step tasks executed in a sandboxed shell environment.

    Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.

Pricing tiers

Claude Opus 5.5: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22.

Grok 4.6: $2/$6 per MTok (<200K prompt); $4/$12 (≥200K). Cached input $0.50/MTok ($1.00 at ≥200K). xAI's release notes list no separate text-output cap (bounded by the 500K context).

FrontierRecord checked September 26, 2026

Claude Opus 5.5

Claude Opus 5.5 is Anthropic's default model for agentic coding and knowledge work — Anthropic says it performs near Fable 5.1 on most work at about 40% lower running cost than Opus 5, and it leads the Artificial Analysis Intelligence Index v4.3.2.

Best for

  • Complex agentic coding
  • Enterprise knowledge work
  • Default frontier model

Watch out

Breaking changes from Opus 5: adaptive thinking cannot be disabled (effort runs low to max, default medium) and forced tool use returns an error. Verbose at max effort, so cap output on cost-sensitive routes.

FrontierRecord checked September 26, 2026

Grok 4.6

Grok 4.6 was xAI's August 2026 coding flagship, superseded by Grok 4.7 (2026-09-21) at the same $2/$6 price.

Best for

  • Coding agents
  • Chat and knowledge
  • Cost-sensitive frontier work

Watch out

Superseded — xAI's docs now say to use Grok 4.7 at the same price. Token rates double above a 200K-token prompt.

When the cheaper one wins

Grok 4.6 is cheaper on output at $6 per million tokens against $20 for Claude Opus 5.5 — about 3.3×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.

Run the model picker

Evidence confidence: High

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

  • Pricing verified on both sides — Input and output rates are verified for both models.
  • 3/5 core specs verified on both sides — Not published for at least one side: max output, parameter count.
  • 1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
  • Verified within the last 90 days — Newest catalog check was 2 days ago.
  • Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

Related comparisons

Diving deeper on one model? Claude Opus 5.5 · Grok 4.6

Common questions

Claude Opus 5.5 vs Grok 4.6

Answered from the verified figures on this page rather than general guidance.

Is Claude Opus 5.5 or Grok 4.6 cheaper for input?
Grok 4.6 is cheaper at $2 per million input tokens, against $4 for Claude Opus 5.5 — roughly 2.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Opus 5.5 has tiered pricing: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22. Grok 4.6 has tiered pricing: $2/$6 per MTok (<200K prompt); $4/$12 (≥200K). Cached input $0.50/MTok ($1.00 at ≥200K). xAI's release notes list no separate text-output cap (bounded by the 500K context).
Is Claude Opus 5.5 or Grok 4.6 cheaper for output?
Grok 4.6 is cheaper at $6 per million output tokens, against $20 for Claude Opus 5.5 — roughly 3.3× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Opus 5.5 has tiered pricing: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22. Grok 4.6 has tiered pricing: $2/$6 per MTok (<200K prompt); $4/$12 (≥200K). Cached input $0.50/MTok ($1.00 at ≥200K). xAI's release notes list no separate text-output cap (bounded by the 500K context).
Which has the larger context window, Claude Opus 5.5 or Grok 4.6?
Claude Opus 5.5 accepts 1M tokens against 500K for Grok 4.6. This only matters if you routinely send very long documents or large codebases.
Do Claude Opus 5.5 and Grok 4.6 support the same reasoning levels?
Claude Opus 5.5 exposes adaptive, while Grok 4.6 exposes low, medium, high, xhigh.
Should I use Claude Opus 5.5 or Grok 4.6?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Opus 5.5 suits complex agentic coding; Grok 4.6 suits coding agents.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

  • Input price: Grok 4.6 costs $2 per 1M tokens versus $4 for Claude Opus 5.5 — a 2x difference at the headline tier.
  • Context: Claude Opus 5.5 takes 1M against 500K for Grok 4.6 — only decisive if your prompts approach the smaller window.
  • Measured capability: Claude Opus 5.5 leads Artificial Analysis Intelligence Index 57.6 to 44.3 (measured 2026-09-26).
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