What Is Claude 2 | Features, Deprecation Status, and Comparison with Claude 3/4

What Is Claude 2 — A Second-Generation Model That Arrived in July 2023

Claude 2 is a large language model announced and released by Anthropic on July 11, 2023 (source: Anthropic Official Blog "Claude 2"). It introduced improvements over the previous Claude 1.3 in coding, mathematical reasoning, and safety, and attracted attention as a leading model compared against OpenAI's GPT-4 at the time.

In a word, Claude 2's positioning was "a second generation focused on contextual understanding and honest responses." While the Claude 1 generation had honed dialogue quality within relatively short contexts, Claude 2 implemented a 100K token (approximately 75,000 words) context window — at the time eight times larger than GPT-4 — and differentiated itself clearly for use cases such as summarizing long documents, analyzing entire codebases, and analyzing full-length novels.

At launch, it was released as a beta in the United States and United Kingdom, before rolling out globally. Business use via API began simultaneously, and it was available on both the free and paid plans (Claude Pro) of claude.ai.

Key Features and Performance Figures for Claude 2.0

Looking at Claude 2.0's performance through official figures, the improvement over the previous Claude 1.3 becomes clear.

In coding performance (HumanEval), scores rose significantly from 56.0% for Claude 1.3 to 71.2% for Claude 2.0. In an environment where GPT-3.5 stood at 48.1% and GPT-4 at 67.0%, Claude 2.0 recorded numbers surpassing GPT-4 on coding-focused evaluations.

In reasoning and knowledge (Bar Exam), performance improved from 73.0% for Claude 1.3 to 76.5% for Claude 2.0. In the GRE reading and writing section, scores exceeded the 90th percentile, demonstrating academic reasoning ability.

In mathematics (GSM8k), scores improved from 85.2% to 88.0%, with enhanced capability for accurately following multi-step numerical calculations.

On safety, Anthropic reported a twofold reduction in harmful responses compared to Claude 1.3. By continuously refining the Constitutional AI approach, the balance between accuracy in refusing inappropriate requests and accuracy in responding to legitimate ones was improved.

The context window of 100K tokens (approximately 75,000 words) was a figure that greatly outpaced competing models of the time. Developers highly valued the ability to feed in PDFs exceeding 500 pages or entire codebases for analysis in a single pass.

Features Added and Improvements in Claude 2.1

Claude 2.1 was announced in November 2023 (source: Anthropic Official Blog "Claude 2.1"). While the update came in under six months from 2.0, it centered on three major improvements.

Improvement 1: Doubled Context Window (200K Tokens)

The context window jumped from 100K in Claude 2.0 to 200K — a full doubling. This corresponds to approximately 150,000 words or 500 pages of documents. It reached a level capable of processing the long-form materials that businesses handle daily, such as financial statements, legal documents, and technical specifications, all at once.

Improvement 2: Significant Reduction in Hallucinations

Hallucinations were reduced by approximately twice compared to Claude 2.0. In particular, errors where the model answers as if it knows something it doesn't were reduced, and responses that honestly convey uncertainty increased. In complex document summarization and interpretation tasks, the incorrect response rate decreased by 30%.

Improvement 3: Addition of Tool Use / Function Calling

A "Tool Use" feature was added, allowing Claude to autonomously select and execute external functions defined by developers via the API. With Claude 2.1, the foundation was established for the first time for performing tasks that a language model cannot complete on its own — such as calculations, API calls, and database searches. This became the prototype for the agent capabilities of the later Claude 3 and Claude 4 generations.

Other Improvements

Customizability of the System Prompt feature was enhanced for developers, and prompt optimization via the Workbench tool became easier. A design was established for fine-tuning model behavior during API usage, accelerating enterprise adoption.

Can Claude 2 Still Be Used? — Deprecation and End-of-Service Status

As of June 2026, Claude 2.0 and Claude 2.1 are not listed in Anthropic's official API model catalog. In Anthropic's official documentation (Models overview), the current models listed are Opus 4.8, Sonnet 4.6, and Haiku 4.5, while legacy models include Opus 4.7 through 4.1 and Sonnet 4 / Opus 4 — but Claude 2.x does not appear even in the "deprecated" section. This means the Claude 2 series has already been fully retired.

The generational transition timeline from Claude 2 → Claude 3 → Claude 4 is roughly as follows:

1. Claude 2.0 released (July 2023)
2. Claude 2.1 released (November 2023) — 200K context, Tool Use added
3. Claude 3 generation (Haiku / Sonnet / Opus) released (March 2024) — surpassed Claude 2.1 significantly across all metrics
4. Claude 3.5 Sonnet released (June 2024) — coding and reasoning standards raised another level
5. Claude 4 generation (Opus 4 / Sonnet 4) released (May 2025) — current flagship generation
6. Claude 2 series API end-of-service (around end of 2025)

If systems built during the Claude 2 era are still running, the model IDs claude-2.0 and claude-2.1 will either return a model_error from the API or are in a state where no response is returned as a deprecated model. Urgent migration to a successor model is necessary.

Performance Comparison with Claude 3 and Claude 4

As of November 2023 when Claude 2.1 was released, it was state-of-the-art — but the gap with subsequent models has widened considerably today.

The comparison in coding performance is telling. Claude 2.0 achieved 71.2% on HumanEval, while Claude 3 Opus (2024) reached 84.9%, and Sonnet 4.6 from the Claude 4 generation handles tasks of an entirely different level of difficulty with a Verified SWE-bench score of 72.7%. SWE-bench is a benchmark evaluating real-world software bug fixes, a domain the Claude 2 generation did not address.

In terms of context window, the Claude 2.1's 200K tokens were matched by Claude 3 Haiku at the same 200K, while Sonnet 4.6 and Opus 4.8 have expanded to 1M tokens (one million tokens). Whereas Claude 2.1's 200K was pioneering at the time, current models can handle five times the context.

In Tool Use (agent capabilities), Claude 2.1 laid the groundwork, but the Claude 4 generation offers a full-fledged agent platform including up to 7 hours of continuous autonomous work, parallel tool calls, and Computer Use (PC operation). Claude 2.1's Tool Use capability can be considered a prototype stage compared to today's agent features.

In terms of pricing, the cost tiers may look similar at a glance, but the Claude 4 generation has significantly improved both token processing efficiency and accuracy at comparable price points. Since using Claude 2.1 no longer works — the API itself is non-functional — please use this comparison as a reference for choosing your migration target.

How to Choose a Current Model to Migrate to from Claude 2

When migrating from the Claude 2 series, which current model to choose depends on your use case. Refer to Anthropic's official model list (Models overview) and use the following criteria to decide.

For general text processing and coding assistance (the main use cases for Claude 2.1), Claude Sonnet 4.6 is the optimal choice. At $3/MTok input and $15/MTok output, it delivers coding accuracy and reasoning capability that far surpasses all of Claude 2.1's abilities. Its 1M token context window also enables large-scale document processing beyond Claude 2.1's 200K.

For maximum-accuracy reasoning and long-running agents, consider Claude Opus 4.8 (input $15/MTok, output $75/MTok). It enables thousands of steps of autonomous task execution and Adaptive Thinking — both impossible with Claude 2.1.

If cost is the top priority and fast responses are required, Claude Haiku 4.5 (input $1/MTok, output $5/MTok) is an option. While it has a 200K token context window, it achieves text comprehension equivalent to or better than Claude 2.1 at lower cost.

Migrating the model ID is technically straightforward:

1. Change the model parameter in your API request from claude-2.1 (or claude-2.0) to the desired model ID (e.g., claude-sonnet-4-6)
2. Run behavior tests with your existing prompts to check for any changes in output format (more detailed responses, different writing style)
3. Since some Claude 4 generation models have changed how temperature / top_p / top_k parameters are handled, if you specify these parameters, refer to Anthropic's migration guide

Summary — The Historical Significance of Claude 2 and Today's Options

Claude 2 (released July 2023) was the generation that established Anthropic as a major player in the large language model space. Its 100K token context window, HumanEval coding score of 71.2%, and Bar Exam reasoning score of 76.5% were meaningful benchmarks for 2023 — but the gap with successor models has grown substantially today.

Claude 2.1 (November 2023) enhanced practicality through its expansion to a 200K context, reduced hallucinations, and the addition of Tool Use — but as of 2026, the API itself is unavailable.

Developers running systems from the Claude 2 era should proceed with migrating to Claude Sonnet 4.6 or Claude Opus 4.8 immediately. In most cases, migration is complete in two steps — replacing the model ID and verifying output differences — enabling operation at equal or higher quality with lower costs.

For detailed comparisons of current models and selection criteria by use case, please also refer to Anthropic's official model list and related articles on Clauder Navi.