GPT-5.5 vs Mistral Large 3 675B Instruct

Name: GPT-5.5
Author: OpenAI

GPT-5.5 (2026) and Mistral Large 3 675B Instruct (2025) are frontier reasoning models from OpenAI and MistralAI. GPT-5.5 ships a 1.05m-token context window, while Mistral Large 3 675B Instruct ships a 128k-token context window. On MMLU PRO, GPT-5.5 leads by 2.6 pts. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.

GPT-5.5 fits 8x more tokens; pick it for long-context work and Mistral Large 3 675B Instruct for tighter calls.

Decision scorecard

Local evidence first

Signal	GPT-5.5	Mistral Large 3 675B Instruct	How to read it
Best for	reasoning-heavy apps, multimodal apps, and tool-calling agents	multimodal apps and provider-routed production	Use-case synthesis from product type, capability flags, context, and provider data.
Decision fit	Coding, RAG, and Agents	Coding, RAG, and Agents	Primary workload tags from local decision data.
Context window	1.05m	128k	Higher is better when prompts, retrieval chunks, or transcripts are large.
Cheapest output	$30/1M tokens	$1.50/1M tokens	Cheapest tracked provider route; verify your exact region and tier.
Provider routes	4 tracked	6 tracked	Broader coverage can reduce vendor lock-in and fallback risk.
Shared benchmarks	MMLU PRO leader	3 shared	Visible benchmark lead is 2.6 points on MMLU PRO.

Decision tradeoffs

Choose GPT-5.5 when...

GPT-5.5 holds a shared-benchmark lead on MMLU PRO, ahead by 2.6 points.
GPT-5.5 has the larger context window for long prompts, retrieval packs, or transcript analysis.
GPT-5.5 uniquely exposes Reasoning, JSON / Tool use, and Code execution in local model data.
Local decision data tags GPT-5.5 for Coding, RAG, and Agents.

Choose Mistral Large 3 675B Instruct when...

Mistral Large 3 675B Instruct has the lower cheapest tracked output price at $1.50/1M tokens.
Mistral Large 3 675B Instruct has broader tracked provider coverage for fallback and route flexibility.
Local decision data tags Mistral Large 3 675B Instruct for Coding, RAG, and Agents.

Monthly cost at traffic

Estimate token spend from the cheapest tracked input and output route or tier on this page.

Lower estimate Mistral Large 3 675B Instruct

Requests / monthInput tokens / requestOutput tokens / request

GPT-5.5

$11,500

Cheapest tracked route/tier: OpenAI API 0-272K input tokens

Mistral Large 3 675B Instruct

$775

Cheapest tracked route/tier: OpenRouter

Estimated monthly gap: $10,725. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.

Switch friction

GPT-5.5 -> Mistral Large 3 675B Instruct

Provider overlap exists on OpenRouter, AWS Bedrock, and Vercel AI Gateway; start route-level A/B tests there.
Mistral Large 3 675B Instruct is $28.50/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
Check replacement coverage for Reasoning, JSON / Tool use, and Code execution before moving production traffic.

Mistral Large 3 675B Instruct -> GPT-5.5

Provider overlap exists on OpenRouter, Vercel AI Gateway, and AWS Bedrock; start route-level A/B tests there.
GPT-5.5 is $28.50/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
GPT-5.5 adds Reasoning, JSON / Tool use, and Code execution in local capability data.

Specs

Specification	GPT-5.5 OpenAI	Mistral Large 3 675B Instruct MistralAI
Released	2026-04-23	2025-12-01
Context window	1.05m	128k
Parameters	—	675B
Architecture	Decoder Only	Decoder Only
License	Proprietary	Apache 2.0OSI-approved
Openness	Proprietary	Open source
Weights	Not released	Unknown
Code	Unknown	Unknown
Commercial use	Commercial use: conditional	Commercial use: permitted
Knowledge cutoff	2025-12	2024-11

Pricing and availability

Pricing attribute	GPT-5.5	Mistral Large 3 675B Instruct
Input price	0-272K input tokens $5/1M tokens Standard GPT-5.5 token pricing before the long-context surcharge threshold. 272K+ input tokens $8/1M tokens Long-context surcharge applies above 272K input tokens for the full session.	$0.50/1M tokens
Output price	0-272K input tokens $30/1M tokens Standard GPT-5.5 token pricing before the long-context surcharge threshold. 272K+ input tokens $36/1M tokens Long-context surcharge applies above 272K input tokens for the full session.	$1.50/1M tokens
Providers	OpenAI API OpenRouter Vercel AI Gateway AWS Bedrock	OpenRouter AWS Bedrock NVIDIA NIM Mistral AI Studio Microsoft Foundry Vercel AI Gateway

Capabilities

Capability	GPT-5.5	Mistral Large 3 675B Instruct
Vision	Yes	Yes
Multimodal	Yes	Yes
Reasoning	Yes	No
JSON / Tool use	Yes	No
Structured outputs	Yes	Yes
Code execution	Yes	No
IDE integration	No	No
Computer use	No	No
Parallel agents	No	No

Benchmarks

Benchmark	GPT-5.5	Mistral Large 3 675B Instruct
MMLU PRO	88.1	85.5
Google-Proof Q&A	93.6	43.9
HumanEval	94.2	92.0

Continue comparing

Model pages

Labs and families

Related comparisons

Popular comparisons for GPT-5.5

Popular comparisons for Mistral Large 3 675B Instruct

Last reviewed: 2026-06-29. Data sourced from public model cards and provider documentation.

Both models

GPT-5.5 Mistral Large 3 675B Instruct