Claude 3 vs Claude 4: What Changed and Why It Matters

The Generation Jump

Claude 3 shipped in March 2024 with the now-familiar Haiku, Sonnet, Opus tier split, a 200K context window, and the older Anthropic price band that pushed Opus to $15 input and $75 output per million tokens. Claude 4 shipped in May 2025 as a structural rewrite — bigger context, lower flagship pricing, native computer use, and meaningfully better tool-use behavior. The two generations are not just different versions of the same product.

Side-by-Side Comparison

Dimension	Claude 3 Family	Claude 4 Family
Top model	Claude 3 Opus	Opus 4.7 (Mythos Preview above it)
Context window	200K tokens	1M tokens (Sonnet 4.6, Opus 4.6+)
Opus pricing	$15 / $75 per Mtok	$5 / $25 per Mtok
Sonnet pricing	$3 / $15 per Mtok	$3 / $15 per Mtok
Haiku pricing	$0.25 / $1.25 per Mtok	$1 / $5 per Mtok
Computer use	Not available	Native support
Tool-use accuracy	Strong	Significantly improved on complex chains
Reasoning benchmarks	Solid on standard tasks	Materially higher on novel problems
Agentic workflows	Workable	Designed for long chains, holds coherence better

What Actually Changed

Context window: The jump from 200K to 1M tokens is the single biggest practical change. You can now load entire mid-sized codebases into context without summarizing or chunking. Long agentic sessions stay coherent because earlier decisions are still in the window. The 200K window of Claude 3 was generous in 2024 but constraining for the workflows people actually built.

Computer use: Claude 4 added native computer use — the ability to take screenshots, click, type, and drive a UI. Claude 3 did not have this capability. If your workflow involves browser automation, testing UIs, or any task that requires interacting with software that does not have a clean API, Claude 4 is the only choice.

Tool-use accuracy: Claude 3 was already strong on tool use, but the failure mode was drift on long chains — the model would forget what tools were available, or call them with the wrong arguments after many turns. Claude 4 holds tool definitions more reliably and recovers from tool errors more gracefully. For Claude Code workflows specifically, this is the difference between sessions that finish and sessions that need babysitting.

Reasoning depth: On benchmarks involving novel problems — not just memorized patterns — Claude 4 models score materially higher. The gap is biggest on multi-constraint problems and weakest on standard transformations where Claude 3 was already near ceiling.

When to Stick with Claude 3

Cost-sensitive workloads where Haiku 3 at $0.25 per million input tokens beats Haiku 4.5 at $1
Simple transformations and classifications where the older models are already at ceiling
Existing production systems with stable behavior that you do not want to perturb
Workflows that do not need the 1M context window or computer use

When to Upgrade to Claude 4

Complex multi-step workflows where reasoning drift was a problem on Claude 3
Large codebases where the 200K window forced summarization
Anything involving computer use, browser automation, or UI testing
Production agentic systems where tool-use reliability matters
Top-tier reasoning at Opus pricing — Opus 4.7 at $5/$25 is now cheaper than Sonnet 3 was at the same workload

Migration Considerations for Claude Code Users

Claude Code is built around the Claude 4 generation. The aliases sonnet, opus, and haiku resolve to Claude 4 models by default. If you were running scripts that pinned to a Claude 3 model ID, audit them — the model is still callable via API but the surrounding Claude Code tooling assumes Claude 4 behavior on tool use and context handling.

The upgrade path is usually as simple as removing the explicit model pin and letting Claude Code default to the current alias. Test once on a non-critical task to confirm the output shape matches expectations, then ship it. The cost will drop, the context window will expand, and the tool-use reliability will improve — all without code changes.