Claude Model Releases: Complete Timeline from Claude 1 to Opus 4.5

Anthropic’s Claude models have evolved rapidly since the first public release in March 2023. In just over two years, the model family has grown from a single release to a tiered system spanning three capability levels—Haiku, Sonnet, and Opus—with increasingly sophisticated reasoning and agentic capabilities.

This post covers every major Claude release with dates, key improvements, and context on how the model family has evolved.

Release Timeline

Release Date	Model	Notes
March 2023	Claude 1	First public release (includes Claude Instant)
July 2023	Claude 2	Second major version
November 2023	Claude 2.1	Expanded context window
March 4, 2024	Claude 3 Haiku	First multi-tier family (fastest)
March 4, 2024	Claude 3 Sonnet	Mid-tier balanced model
March 4, 2024	Claude 3 Opus	Highest-tier flagship
June 20, 2024	Claude 3.5 Sonnet	Major performance upgrade
October 2024	Claude 3.5 Haiku	Faster 3.5 variant
February 24, 2025	Claude 3.7 Sonnet	Hybrid reasoning introduction
May 22–23, 2025	Claude 4 Opus	Next-gen flagship
May 22–23, 2025	Claude 4 Sonnet	Companion to Opus 4
August 5, 2025	Claude Opus 4.1	Refined Opus 4
September 29–30, 2025	Claude Sonnet 4.5	High-intelligence mid-tier
October 15, 2025	Claude Haiku 4.5	Fast, cost-efficient
November 24, 2025	Claude Opus 4.5	Most advanced model

Notes:

• Claude Instant iterations (e.g., Instant 1.2) were part of the 2023 line but are captured at the family level
• Claude 3.5 Opus was never formally released as a standalone model

Detailed Changelog

March 2023 — Claude 1 / Claude Instant

• First public release of Anthropic’s Claude models
• Strong focus on safety, helpfulness, and long-context conversation
• Claude Instant introduced as a faster, cheaper variant

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July 2023 — Claude 2

• Major capability upgrade over Claude 1
• Improved reasoning, writing quality, and coding ability
• Much larger usable context window compared to v1

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November 2023 — Claude 2.1

• Expanded context window (up to ~200k tokens)
• Better long-document understanding and summarization
• Refinements rather than a full generational jump

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March 4, 2024 — Claude 3 Family (Haiku, Sonnet, Opus)

The Claude 3 launch marked a fundamental shift to a tiered model family:

• Haiku: Fastest and cheapest, optimized for high-volume tasks
• Sonnet: Balanced performance and cost for most use cases
• Opus: Highest intelligence and reasoning depth

Key improvements:

• Significant leap in reasoning, math, coding, and vision tasks
• First Claude models with multimodal (image) capabilities

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June 20, 2024 — Claude 3.5 Sonnet

• Noticeable intelligence boost over Claude 3 Sonnet
• Better instruction following and coding accuracy
• Became the default “go-to” Claude for many users
• Introduced computer use capabilities

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October 2024 — Claude 3.5 Haiku

• Faster and more capable than Claude 3 Haiku
• Improved efficiency while keeping low latency
• Targeted real-time and high-throughput use cases

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February 24, 2025 — Claude 3.7 Sonnet

• Introduction of hybrid reasoning modes (extended thinking)
• Improved step-by-step reasoning without major latency increase
• Bridge model between Claude 3.x and Claude 4

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May 22–23, 2025 — Claude 4 (Opus & Sonnet)

Major next-generation release:

• Strong emphasis on agentic behavior and tool use
• Better long-horizon reasoning and task persistence
• Opus positioned as flagship reasoning model
• Significant improvements in coding and complex problem-solving

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August 5, 2025 — Claude Opus 4.1

• Refinement of Claude 4 Opus
• Better reliability and consistency
• Incremental intelligence gains rather than new features

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September 29–30, 2025 — Claude Sonnet 4.5

• Significant intelligence upgrade for Sonnet tier
• Approached Opus-level performance on many tasks
• Strong focus on agents, workflows, and production use

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October 15, 2025 — Claude Haiku 4.5

• Major speed and efficiency improvements
• Best-performing small Claude model to date
• Optimized for low-cost, high-volume usage

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November 24, 2025 — Claude Opus 4.5

• Most capable Claude model released
• Best performance for coding, agents, and complex reasoning
• Culmination of the Claude 4.x generation

Evolution Patterns

Looking at the timeline, several patterns emerge:

Single models → Tiered families: Claude 1 and 2 were single models. Claude 3 introduced the Haiku/Sonnet/Opus tiers that continue today.

Increasing agentic focus: After 2024, releases increasingly emphasized tool use, long-running tasks, and autonomous operation.

Rapid iteration: Roughly one major upgrade every 2–3 months, with the pace accelerating in 2025.

Hybrid reasoning: Starting with Claude 3.7 Sonnet, models gained the ability to “think” longer on complex problems before responding.

Model ID Reference

For developers, here are the current model IDs:

Model	API ID
Claude Opus 4.5	claude-opus-4-5-20251101
Claude Sonnet 4.5	claude-sonnet-4-5-20241022
Claude Haiku 4.5	claude-haiku-4-5-20241022

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Last updated: January 2026