1M context vs 200k context: A structural shift
Claude 3.7 Sonnet offers a 200k token context window, sufficient for individual modules but constraining for full-stack monorepos. Claude Sonnet 5.5 expands this to a true 1,000,000 token active memory. In Cursor and Claude Code, this allows entire documentation suites, database schemas, and multiple package directories to reside continuously in context without aggressive lossy pruning.
Agent autonomy and drift resistance
When coding agents execute 20+ consecutive tool calls (bash, grep, edit, test), earlier reasoning passes often suffer semantic drift. Sonnet 5.5 demonstrates higher anchor retention in multi-file refactors, reducing the tendency to rewrite unchanged files or misplace imports. Claude 3.7 remains exceptional, but 5.5 delivers higher one-shot completion rates on complex SWE-bench-style tasks.
Pricing parity and cost calculations
Both models sit at $3.00 input and $15.00 output per million tokens. Prompt caching delivers up to 90% discount on cache hits across both tiers. Because the pricing tier is identical, the financial risk of upgrading is zero. The only variable is prompt cache TTL management in long terminal sessions.
Migration guide for development teams
Set `model: anthropic-claude-sonnet-5-5` in your `.cursorrules`, `claude.json`, or environment variables. Run a smoke test on your CI agent pipeline. Unless you have hardcoded API parameter validations for Claude 3.7's thinking token limits, the transition is completely drop-in.