GPT-4.5 vs GPT-5.1 Instant
GPT-5.1 Instant significantly outperforms across most benchmarks. GPT-5.1 Instant is 27.3x cheaper per token.
OpenAI · OpenAI · Updated for 2026
Which is better?
GPT-4.5 outperforms in 0 benchmarks, while GPT-5.1 Instant is better at 3 benchmarks (GPQA, MMMU, SWE-Bench Verified). GPT-5.1 Instant significantly outperforms across most benchmarks.
On price, GPT-5.1 Instant is roughly 27.3x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
GPT-5.1 Instant also accepts a larger context window (400,000 input tokens), making it the stronger choice for long documents and large codebases.
Based on current benchmark, pricing, and model metadata for 2026.
Choose GPT-4.5
- you want predictable pricing at $75.00/M input and $150.00/M output
Choose GPT-5.1 Instant
- you want the strongest raw capability — it leads on 3 of 3 shared benchmarks
- cost matters — it's about 27.3x cheaper per token
- you process long inputs — it offers a 400,000 token context window
- you want the most recent training data — it shipped Nov 2025
At a glance
The differences that matter most.
Performance Benchmarks
Comparative analysis across standard metrics
GPT-4.5 outperforms in 0 benchmarks, while GPT-5.1 Instant is better at 3 benchmarks (GPQA, MMMU, SWE-Bench Verified).
GPT-5.1 Instant significantly outperforms across most benchmarks.
Arena Performance
Playground indexes and blind preference scores
Pricing Analysis
Price comparison per million tokens
For input processing, GPT-4.5 ($75.00/1M tokens) is 60.0x more expensive than GPT-5.1 Instant ($1.25/1M tokens).
For output processing, GPT-4.5 ($150.00/1M tokens) is 15.0x more expensive than GPT-5.1 Instant ($10.00/1M tokens).
In conclusion, GPT-4.5 is more expensive than GPT-5.1 Instant.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
GPT-5.1 Instant accepts 400,000 input tokens compared to GPT-4.5's 128,000 tokens. GPT-5.1 Instant can generate longer responses up to 128,000 tokens, while GPT-4.5 is limited to 4,096 tokens.
Input Capabilities
Supported data types and modalities
Both GPT-4.5 and GPT-5.1 Instant support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
GPT-4.5
GPT-5.1 Instant
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
GPT-4.5 was released on 2025-02-27, while GPT-5.1 Instant was released on 2025-11-12.
GPT-5.1 Instant is 9 months newer than GPT-4.5.
Feb 27, 2025
1.5 years ago
Nov 12, 2025
9 months ago
8mo newerKnowledge Cutoff
When training data ends
Neither model specifies a knowledge cutoff date.
Unable to compare the recency of their training data.
Provider Availability
GPT-4.5 is available from OpenAI. GPT-5.1 Instant is available from OpenAI.
GPT-4.5
GPT-5.1 Instant
Outputs Comparison
Judge for yourself.
Run your own prompts against GPT-4.5 and GPT-5.1 Instant side-by-side, then vote on the output you prefer.
FAQ
Common questions about GPT-4.5 vs GPT-5.1 Instant.