What is the context window size for Claude 1 and Claude Sonnet 4.5?

Claude 1 has a context window of 9,000 tokens, while Claude Sonnet 4.5 offers a much larger window of 200,000 tokens. This difference allows Sonnet 4.5 to handle far longer inputs, such as extensive codebases or documents, without needing to truncate or chunk the text.

Are the weights of Claude 1 and Claude Sonnet 4.5 publicly available?

Neither Claude 1 nor Claude Sonnet 4.5 has publicly released weights. Both models are distributed only through Anthropic’s API or approved partnerships, meaning users cannot download, modify, or fine‑tune the underlying parameters themselves. This approach aligns with Anthropic’s focus on safety and controlled deployment, ensuring that the models are used under conditions that mitigate misuse while still providing access to their capabilities via the provided interfaces.

Which model supports multimodal input, and what does that mean?

Claude Sonnet 4.5 supports multimodal input, meaning it can process both text and images in the same prompt. Claude 1 is text‑only and cannot interpret visual content directly. This capability enables tasks such as describing photographs, extracting information from diagrams, or generating code based on visual mockups, which are not possible with a purely text‑only model.

What are the primary use cases highlighted for each model?

Claude 1 is positioned as a helpful assistant for general conversation and long‑context reasoning tasks. Claude Sonnet 4.5 emphasizes agentic coding, computer‑use automation, and multimodal understanding, targeting developers and power users who need the model to act autonomously. These use cases reflect the model’s increased context window and tool‑use abilities, allowing it to manage complex software engineering workflows that exceed the scope of a standard conversational assistant.

Do both models have the same developer and licensing approach?

Yes, both Claude 1 and Claude Sonnet 4.5 are developed by Anthropic and neither offers open weights. Users access them through Anthropic’s provided services rather than downloading the model files. This licensing strategy ensures that Anthropic can maintain oversight over model deployment, updates, and safety measures while still offering scalable access via APIs or partner integrations.

Comparison · Updated Aug 24, 2026

Claude 1 vs Claude Sonnet 4.5

Claude 1 is Anthropic’s first public LLM with a 9k‑token context; Claude Sonnet 4.5 expands to 200k tokens, adds multimodal input and agentic coding features.

Model A

Claude 1

First public Claude model from Anthropic.

Mar 14, 2023

Model B

Claude Sonnet 4.5

Anthropic's coding- and agent-focused flagship in the Claude 4 family.

Sep 29, 2025

Differences

Attribute	Claude 1	Claude Sonnet 4.5
Developer	Anthropic	Anthropic
Released	2023-03-14	2025-09-29
Open weights	false	false
Modality	text only	text and image
Context window	9,000 tokens	200,000 tokens
Capabilities	helpful assistant, long context	agentic coding, computer use
Best for	general assistance and conversation	coding agents, computer‑use tasks, multimodal understanding

Verdict

Readers seeking a straightforward, helpful assistant with moderate context should choose Claude 1. Those needing extensive context, multimodal input, or agentic coding capabilities will benefit more from Claude Sonnet 4.5.

Analysis

Overview Claude 1 and Claude Sonnet 4.5 are both large language models developed by Anthropic. Claude 1, released in March 2023, was the first public model in the Claude series and is designed as a helpful assistant with a relatively modest context window. Claude Sonnet 4.5, released in September 2025, represents a later flagship in the Claude 4 family, emphasizing agentic behavior, coding assistance, and multimodal understanding.

Where they differ The most notable differences lie in context length, modality, and intended capabilities. Claude 1 offers a context window of 9,000 tokens, whereas Claude Sonnet 4.5 expands this to 200,000 tokens, allowing it to process much longer documents or codebases in a single prompt. Modality also diverges: Claude 1 accepts only text input, while Claude Sonnet 4.5 is multimodal, capable of interpreting images alongside text. In terms of capabilities, Claude 1 is positioned as a general-purpose helpful assistant, excelling at conversation and long‑context reasoning. Claude Sonnet 4.5 adds agentic coding features and the ability to perform computer‑use tasks, targeting developers and users who need the model to act autonomously within software environments. Both models share the same developer, Anthropic, and neither releases its weights publicly.

Which to choose If you need a reliable conversational assistant that can handle moderate‑length contexts and you do not require image understanding or autonomous tool use, Claude 1 remains a solid choice. Conversely, if your workflow involves processing extensive texts or code, interpreting visual information, or having the model carry out agentic actions such as writing and editing code or interacting with a computer interface, Claude Sonnet 4.5 provides the necessary scale and functionality. The decision ultimately hinges on whether the extra context, multimodal input, and agentic features justify moving to the newer model.

Frequently asked

What is the context window size for Claude 1 and Claude Sonnet 4.5?: Claude 1 has a context window of 9,000 tokens, while Claude Sonnet 4.5 offers a much larger window of 200,000 tokens. This difference allows Sonnet 4.5 to handle far longer inputs, such as extensive codebases or documents, without needing to truncate or chunk the text.
Are the weights of Claude 1 and Claude Sonnet 4.5 publicly available?: Neither Claude 1 nor Claude Sonnet 4.5 has publicly released weights. Both models are distributed only through Anthropic’s API or approved partnerships, meaning users cannot download, modify, or fine‑tune the underlying parameters themselves. This approach aligns with Anthropic’s focus on safety and controlled deployment, ensuring that the models are used under conditions that mitigate misuse while still providing access to their capabilities via the provided interfaces.
Which model supports multimodal input, and what does that mean?: Claude Sonnet 4.5 supports multimodal input, meaning it can process both text and images in the same prompt. Claude 1 is text‑only and cannot interpret visual content directly. This capability enables tasks such as describing photographs, extracting information from diagrams, or generating code based on visual mockups, which are not possible with a purely text‑only model.
What are the primary use cases highlighted for each model?: Claude 1 is positioned as a helpful assistant for general conversation and long‑context reasoning tasks. Claude Sonnet 4.5 emphasizes agentic coding, computer‑use automation, and multimodal understanding, targeting developers and power users who need the model to act autonomously. These use cases reflect the model’s increased context window and tool‑use abilities, allowing it to manage complex software engineering workflows that exceed the scope of a standard conversational assistant.
Do both models have the same developer and licensing approach?: Yes, both Claude 1 and Claude Sonnet 4.5 are developed by Anthropic and neither offers open weights. Users access them through Anthropic’s provided services rather than downloading the model files. This licensing strategy ensures that Anthropic can maintain oversight over model deployment, updates, and safety measures while still offering scalable access via APIs or partner integrations.