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Model comparison

Claude Opus 5.5 vs Mistral Medium 3.5

Anthropic against Mistral, 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

Mistral

Mistral Medium 3.5

Frontier · Open weights

AI model capability comparison
SpecificationClaude Opus 5.5Mistral Medium 3.5
ProviderAnthropicMistral
TierFrontierFrontier
Context windowWinner: 1M262K
Max output128KNot verifiedUnverified
Input / 1M tokens$4Winner: $1.50
Output / 1M tokens$20Winner: $7.50
WeightsClosedOpen
ParametersNot disclosedUnverified128B dense
Reasoning levelsadaptiveNot verifiedUnverified
Modalitiestext, imagetext, image
LicenseNot disclosedUnverifiedModified MIT
API model idclaude-opus-5-5mistral-medium-3-5
ReleasedSeptember 22, 2026April 28, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)57.6Not verifiedUnverified
Artificial Analysis Intelligence Index (2026-09-26)Not verifiedUnverified14.2
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

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.

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.

Mistral Medium 3.5: Mistral first-party API $1.50/$7.50 per MTok; Mistral advertises up to 90% off cached input (exact cached rate not verified). Open weights under a Modified MIT licence. 128B dense.

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.

FrontierOpen weightsRecord checked September 26, 2026

Mistral Medium 3.5

Mistral Medium 3.5 is the model Mistral calls its new flagship — a 128B dense open-weight model with a 256K context, powering its Vibe remote agents.

Best for

  • EU-hosted frontier work
  • Open-weight self-hosting
  • Mistral Vibe agents

Watch out

Far behind US and Chinese frontier models on the Artificial Analysis index; max output is not published. Check the Modified MIT terms before redistribution.

When the cheaper one wins

Mistral Medium 3.5 is cheaper on output at $7.50 per million tokens against $20 for Claude Opus 5.5 — about 2.7×. 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.
  • 2/5 core specs verified on both sides — Not published for at least one side: max output, parameter count, reasoning levels.
  • 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 · Mistral Medium 3.5

Common questions

Claude Opus 5.5 vs Mistral Medium 3.5

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

Is Claude Opus 5.5 or Mistral Medium 3.5 cheaper for input?
Mistral Medium 3.5 is cheaper at $1.50 per million input tokens, against $4 for Claude Opus 5.5 — roughly 2.7× 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. Mistral Medium 3.5 has tiered pricing: Mistral first-party API $1.50/$7.50 per MTok; Mistral advertises up to 90% off cached input (exact cached rate not verified). Open weights under a Modified MIT licence. 128B dense.
Is Claude Opus 5.5 or Mistral Medium 3.5 cheaper for output?
Mistral Medium 3.5 is cheaper at $7.50 per million output tokens, against $20 for Claude Opus 5.5 — roughly 2.7× 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. Mistral Medium 3.5 has tiered pricing: Mistral first-party API $1.50/$7.50 per MTok; Mistral advertises up to 90% off cached input (exact cached rate not verified). Open weights under a Modified MIT licence. 128B dense.
Which has the larger context window, Claude Opus 5.5 or Mistral Medium 3.5?
Claude Opus 5.5 accepts 1M tokens against 262K for Mistral Medium 3.5. This only matters if you routinely send very long documents or large codebases.
Should I use Claude Opus 5.5 or Mistral Medium 3.5?
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; Mistral Medium 3.5 suits eu-hosted frontier work.
Can I self-host Claude Opus 5.5 or Mistral Medium 3.5?
Mistral Medium 3.5 publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. Claude Opus 5.5 is a closed model whose supported access paths are controlled by its provider.

Next step

Choosing between them

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

  • Input price: Mistral Medium 3.5 costs $1.50 per 1M tokens versus $4 for Claude Opus 5.5 — a 2.7x difference at the headline tier.
  • Context: Claude Opus 5.5 takes 1M against 262K for Mistral Medium 3.5 — only decisive if your prompts approach the smaller window.
  • Measured capability: Claude Opus 5.5 leads Artificial Analysis Intelligence Index 57.6 to 14.2 (measured 2026-09-26).
  • Deployment: Mistral Medium 3.5 publishes weights you can self-host; the other is API-only.
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