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Grok 4 Fast vs Phi-3.5 Mini 128K Instruct (Comparative Analysis)

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Comparative Analysis: Grok 4 Fast vs. Phi-3.5 Mini 128K Instruct
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Overview

Phi-3.5 Mini 128K Instruct was released 1 year before Grok 4 Fast.
Grok 4 FastGrok 4 Fast
Phi-3.5 Mini 128K InstructPhi-3.5 Mini 128K Instruct
Model Provider
The organization behind this AI's development
XAI logoXAI
Microsoft logoMicrosoft
Input Context Window
Maximum input tokens this model can process at once
2M
tokens
128K
tokens
Output Token Limit
Maximum output tokens this model can generate at once
30K
tokens
Not specified
tokens
Release Date
When this model first became publicly available
September 19th, 2025
August 21st, 2024

Capabilities & Features

Compare supported features, modalities, and advanced capabilities
Grok 4 Fast
Phi-3.5 Mini 128K Instruct
Input Types
Supported input formats
📝Text🖼️Image
📝Text
Output Types
Supported output formats
📝Text
📝Text
Tokenizer
Text encoding system
GrokOther
Key Features
Advanced capabilities
Function CallingStructured OutputReasoning ModeContent Moderation
Function CallingStructured OutputReasoning ModeContent Moderation
Open Source
Model availability
ProprietaryAvailable on HuggingFace →

Pricing

Grok 4 Fast is roughly 2.0x more expensive compared to Phi-3.5 Mini 128K Instruct for input tokens and roughly 5.0x more expensive for output tokens.
Grok 4 FastGrok 4 Fast
Phi-3.5 Mini 128K InstructPhi-3.5 Mini 128K Instruct
Input Token Cost
Cost per million input tokens
$0.20
per million tokens
$0.10
per million tokens
Output Token Cost
Cost per million outut tokens
$0.50
per million tokens
$0.10
per million tokens

Benchmarks

Compare relevant benchmarks between Grok 4 Fast and Phi-3.5 Mini 128K Instruct.
Grok 4 FastGrok 4 Fast
Phi-3.5 Mini 128K InstructPhi-3.5 Mini 128K Instruct
MMLU
Measures knowledge across 57 subjects like law, math, history, and science
Benchmark not available.
Benchmark not available.
MMMU
Measures understanding of combined text and images across various domains
Benchmark not available.
Benchmark not available.
HellaSwag
Measures common sense reasoning by having models complete sentences about everyday situations
Benchmark not available.
Benchmark not available.

At a Glance

Quick overview of what makes Grok 4 Fast and Phi-3.5 Mini 128K Instruct unique.
XAI logoGrok 4 Fast by XAI understands both text and images, can use external tools and APIs, offers advanced reasoning, generates structured data. It can handle standard conversations with its 2M token context window. Very affordable at $0.20/M input and $0.50/M output tokens. Released September 19th, 2025.
Microsoft logoPhi-3.5 Mini 128K Instruct by Microsoft can use external tools and APIs. It can handle standard conversations with its 128K token context window. Very affordable at $0.10/M input and $0.10/M output tokens. Released August 21st, 2024.

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