Claude 3.5 Sonnet shifts how developers manage large code migrations with 200k context

Effective recall matters more than vanity metrics like raw context length. When processed with 50k-token technical docs, Claude 3.5 Sonnet extracts precise logic from the middle of large prompts more sharply than competitors. GPT-4o starts omitting sections or hallucinating if a single prompt surpasses the 30k-40k range. While Gemini 1.5 Pro handles a million tokens, it often lazily points to information locations rather than synthesizing answers, adding an extra step for the user.

Gemini 1.5 Pro is described in its documentation as a formidable tool for large-scale code migrations because it can process up to one million tokens. Despite this, Claude 3.5 Sonnet remains more effective for migrations due to its grasp of precise logic. It follows complex instructions hidden within 100k-token dumps, while GPT-4o suffers from "middle-loss" and returns generic training data when vital info is buried in a long prompt. Claude 3.5 Sonnet offers cost savings via context caching, though the web UI lags during long histories unless the API is used.

The Mythos-class Fable 5 model, launched for general use, exceeds all previous generally available models, especially as tasks grow in complexity. To prevent cybersecurity misuse, safeguards route certain queries to Claude Opus 4. After being announced Jun 9, 2026, and temporarily suspended Jun 12, 2026, Claude Fable 5 and Claude Mythos 5 were redeployed Jul 1, 2026.

To improve results, group the entire relevant module and interface definitions in one block using XML tags. This prevents the model from confusing variable names across different files:

<codebase>
  <file path="src/auth.ts"> [Insert Code Here] </file>
  <file path="src/user_service.ts"> [Insert Code Here] </file>
</codebase>

Choose Claude for synthesis and logic, Gemini for searching for a needle in a haystack, and GPT-4o for iterating on small snippets.