Anthropic ships 1M context window for Claude Opus at no extra cost

Context window expansion for Claude Opus

Anthropic has shipped the 1 million token context window for Claude Opus to all Claude Code users on Max, Team, and Enterprise plans in version 2.1.75. Previously, users had to pay extra usage fees for the 1M window, but it's now included at no additional cost on those plans.

Practical implications

The default context window remains 200k tokens, making the 1M window 5x larger. This capacity translates to approximately:

• ~750k words
• ~75k lines of code
• The entire Harry Potter series
• The full source of a mid-sized open-source project, or several smaller ones (e.g., Express.js + Flask + FastAPI together)

Users report that this changes their workflow significantly. For research tasks, they can now feed more details into context, such as using exa MCP to fetch full web pages into context instead of relying on built-in web fetch summaries.

Benefits and limitations

The expanded context window means:

• No need to compact prompts for bigger tasks that still fit within 1M tokens
• Ability to throw entire projects into context, allowing the model to see all files and dependencies, potentially reducing errors

However, the source notes that 1M tokens doesn't mean 1M tokens of real attention. In practice, only about 50–65% of the window is used effectively, and more context still means more diluted attention.