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Model comparison

GPT-5.3-Codex vs Mistral Medium 3.5

OpenAI 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

OpenAI

GPT-5.3-Codex

Frontier

vs

Mistral

Mistral Medium 3.5

Frontier · Open weights

AI model capability comparison
SpecificationGPT-5.3-CodexMistral Medium 3.5
ProviderOpenAIMistral
TierFrontierFrontier
Context windowWinner: 400K262K
Max output128KNot verifiedUnverified
Input / 1M tokens$1.75Winner: $1.50
Output / 1M tokens$14Winner: $7.50
WeightsClosedOpen
ParametersNot disclosedUnverified128B dense
Reasoning levelslow, medium, high, xhighNot verifiedUnverified
Modalitiestext, imagetext, image
LicenseNot disclosedUnverifiedModified MIT
API model idgpt-5.3-codexmistral-medium-3-5
ReleasedFebruary 5, 2026April 28, 2026
Artificial Analysis Intelligence Index [xhigh] (2026-09-26)32.5Not verifiedUnverified
Artificial Analysis Intelligence Index (2026-09-26)Not verifiedUnverified14.2

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

    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.

Pricing tiers

GPT-5.3-Codex: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Still listed in the API as a coding-specialised model.

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

GPT-5.3-Codex

GPT-5.3-Codex is OpenAI's coding-specialised API model at $1.75/$14 — the Codex agent itself now runs GPT-6 Sol, Luna and Astra.

Best for

  • Autonomous coding
  • Repo-scale refactors
  • Test generation

Watch out

Tuned for coding, not general chat; for new coding work compare GPT-6 Sol ($2/$10) first.

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 $14 for GPT-5.3-Codex — about 1.9×. 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.

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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? GPT-5.3-Codex · Mistral Medium 3.5

Common questions

GPT-5.3-Codex vs Mistral Medium 3.5

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

Is GPT-5.3-Codex or Mistral Medium 3.5 cheaper for input?
Mistral Medium 3.5 is cheaper at $1.50 per million input tokens, against $1.75 for GPT-5.3-Codex — roughly 1.2× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.3-Codex has tiered pricing: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Still listed in the API as a coding-specialised model. 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 GPT-5.3-Codex or Mistral Medium 3.5 cheaper for output?
Mistral Medium 3.5 is cheaper at $7.50 per million output tokens, against $14 for GPT-5.3-Codex — roughly 1.9× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.3-Codex has tiered pricing: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Still listed in the API as a coding-specialised model. 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, GPT-5.3-Codex or Mistral Medium 3.5?
GPT-5.3-Codex accepts 400K tokens against 262K for Mistral Medium 3.5. This only matters if you routinely send very long documents or large codebases.
Should I use GPT-5.3-Codex or Mistral Medium 3.5?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. GPT-5.3-Codex suits autonomous coding; Mistral Medium 3.5 suits eu-hosted frontier work.
Can I self-host GPT-5.3-Codex 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. GPT-5.3-Codex 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 $1.75 for GPT-5.3-Codex — a 1.2x difference at the headline tier.
  • Context: GPT-5.3-Codex takes 400K against 262K for Mistral Medium 3.5 — only decisive if your prompts approach the smaller window.
  • Deployment: Mistral Medium 3.5 publishes weights you can self-host; the other is API-only.
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